import java.math.*;
import java.util.*;
import java.io.*;
  
public class Main { 
  
    static BufferedReader in;
    static PrintWriter out = new PrintWriter(System.out);
    static String file = "../in";
    static int test = 10; // 0 for local testing, 1 for std input
    static int inf = 1_000_000, mod = 1_000_000_007;



    void swap(int[]ary, int i, int j)
    {
        int t = ary[i];
        ary[i] = ary[j];
        ary[j] = t;
    }
    
    String[] split() throws Exception
    {
        return in.readLine().split(" ");
    }

    int readInt() throws Exception
    {
        return Integer.valueOf(in.readLine());
    }

    long readLong() throws Exception
    {
        return Long.valueOf(in.readLine());
    }

    long[] toLongArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        long[] ary = new long[n];
        for(int i = 0; i < n; i++) ary[i] = Long.valueOf(sp[i]);
        return ary;
    }

    int[] toIntArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        int[] ary = new int[n];
        for(int i = 0; i < n; i++) ary[i] = Integer.valueOf(sp[i]);
        return ary;
    }

    String reverse(String str)
    {
        return new StringBuilder(str).reverse().toString();
    }


    long pow(long a, int pow)
    {
        long res = 1;
        while(pow > 0)
        {
            if(pow % 2 != 0) {
                res *= a;
                res %= mod;
            }
            a = a * a;
            a %= mod;
            pow /= 2;
        }

        return res;
    }

    public static void main(String[] args) throws Exception
    {
        int _k = Integer.valueOf("1");
        if(test > 0) in = new BufferedReader(new InputStreamReader(System.in));
        else in = new BufferedReader(new FileReader(file));
        if(test < 0) {String[] str = in.readLine().split(" ");
        char[] gg = in.readLine().toCharArray();}
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
        // System.out.println((-100 + 0) / 2);

        // char[] c = new char[4];
        // c[1] = '.';
        // for(char i = '0'; i <= '9'; i++)
        // {
        //     for(char j = '0'; j <= '9'; j++)
        //     {
        //         for(char k = '0'; k <= '9'; k++)
        //         {
        //             c[0] = i;
        //             c[2] = j;
        //             c[3] = k;
        //             double d = Double.valueOf(String.valueOf(c));
        //             int v = (int)(d * 100);
        //             String s1 = String.valueOf("" + c[0] + c[2] + c[3]),
        //                 s2 = String.valueOf(v);
        //             System.out.printf("%s %s %b\n", s1, s2, s1.equals(s2));
        //         }
        //     }
        // }


        new Main().b();
        out.flush();
    }
    void f() throws Exception
    {
        int k = readInt();
        String s = in.readLine();
        int n = s.length();
        long prod = 1;
        int mod = 1_000_000_007;
        for(int i = 0; i < k; i++)
        {
            n++;
            prod = (prod * 26 * n) % mod;
        }
        System.out.println(prod);

    }

    void e() throws Exception
    {
        int n = readInt();
        int[] ary = toIntArray();
        int xor = 0;
        for(int k : ary) xor ^= k;
        for(int i = 0; i < n; i++)
        {
            ary[i] ^= xor;
        }
        for(int k : ary) out.printf("%d ", k);
        
    }

    void d() throws Exception
    {
        long n = readLong();
        long[] ary = toLongArray();
        long[] f = new long[100010];
        long sum = 0;
        for(long k : ary)
        {
            f[(int)k]++;
            sum += k;
        }
        long q = readLong();
        while(q--> 0)
        {
            long[] op = toLongArray();
            long b = op[0], c = op[1];
            long count = f[(int)b];
            sum = sum - b * count + c * count;
            f[(int)b] -= count;
            f[(int)c] += count;
            System.out.println(sum);
        }
    }

    int count(int k)
    {
        int sum = 0, cur = 0;
        while(sum + cur <= k)
        {
            sum += cur;
            cur++;
        }
        return cur - 1;
    }


    void c() throws Exception
    {
        long n = readLong();
        StringBuilder sb = new StringBuilder();
        String str = "";
        while(n > 0)
        {
            long rem = n % 26;
            if(rem == 0) rem = 26;
            n = (n - rem) / 26;
            str = (char)('a' + rem - 1) + str;
        }
        System.out.println(str);
    }

    int gcd(int a, int b)
    {
        if(b == 0) return a;
         return gcd(b, a % b);
    }

    void b() throws Exception
    {
        String s1 = in.readLine(),
                s2 = in.readLine();
        int n = s1.length();
        int ans = 0;
        for(int i = 0; i < n; i++)
        {
            char c1 = s1.charAt(i),
                c2 = s2.charAt(i);
            if(c1 != c2) ans++;
        }
        out.println(ans);
    }

    void a() throws Exception
    {
        int a = readInt();
        out.println(a + a * a + a * a * a);
    }
} import java.math.*; math.* java import java.util.*; util.* java import java.io.*; io.* java public class Main { 
  
    static BufferedReader in;
    static PrintWriter out = new PrintWriter(System.out);
    static String file = "../in";
    static int test = 10; // 0 for local testing, 1 for std input
    static int inf = 1_000_000, mod = 1_000_000_007;



    void swap(int[]ary, int i, int j)
    {
        int t = ary[i];
        ary[i] = ary[j];
        ary[j] = t;
    }
    
    String[] split() throws Exception
    {
        return in.readLine().split(" ");
    }

    int readInt() throws Exception
    {
        return Integer.valueOf(in.readLine());
    }

    long readLong() throws Exception
    {
        return Long.valueOf(in.readLine());
    }

    long[] toLongArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        long[] ary = new long[n];
        for(int i = 0; i < n; i++) ary[i] = Long.valueOf(sp[i]);
        return ary;
    }

    int[] toIntArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        int[] ary = new int[n];
        for(int i = 0; i < n; i++) ary[i] = Integer.valueOf(sp[i]);
        return ary;
    }

    String reverse(String str)
    {
        return new StringBuilder(str).reverse().toString();
    }


    long pow(long a, int pow)
    {
        long res = 1;
        while(pow > 0)
        {
            if(pow % 2 != 0) {
                res *= a;
                res %= mod;
            }
            a = a * a;
            a %= mod;
            pow /= 2;
        }

        return res;
    }

    public static void main(String[] args) throws Exception
    {
        int _k = Integer.valueOf("1");
        if(test > 0) in = new BufferedReader(new InputStreamReader(System.in));
        else in = new BufferedReader(new FileReader(file));
        if(test < 0) {String[] str = in.readLine().split(" ");
        char[] gg = in.readLine().toCharArray();}
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
        // System.out.println((-100 + 0) / 2);

        // char[] c = new char[4];
        // c[1] = '.';
        // for(char i = '0'; i <= '9'; i++)
        // {
        //     for(char j = '0'; j <= '9'; j++)
        //     {
        //         for(char k = '0'; k <= '9'; k++)
        //         {
        //             c[0] = i;
        //             c[2] = j;
        //             c[3] = k;
        //             double d = Double.valueOf(String.valueOf(c));
        //             int v = (int)(d * 100);
        //             String s1 = String.valueOf("" + c[0] + c[2] + c[3]),
        //                 s2 = String.valueOf(v);
        //             System.out.printf("%s %s %b\n", s1, s2, s1.equals(s2));
        //         }
        //     }
        // }


        new Main().b();
        out.flush();
    }
    void f() throws Exception
    {
        int k = readInt();
        String s = in.readLine();
        int n = s.length();
        long prod = 1;
        int mod = 1_000_000_007;
        for(int i = 0; i < k; i++)
        {
            n++;
            prod = (prod * 26 * n) % mod;
        }
        System.out.println(prod);

    }

    void e() throws Exception
    {
        int n = readInt();
        int[] ary = toIntArray();
        int xor = 0;
        for(int k : ary) xor ^= k;
        for(int i = 0; i < n; i++)
        {
            ary[i] ^= xor;
        }
        for(int k : ary) out.printf("%d ", k);
        
    }

    void d() throws Exception
    {
        long n = readLong();
        long[] ary = toLongArray();
        long[] f = new long[100010];
        long sum = 0;
        for(long k : ary)
        {
            f[(int)k]++;
            sum += k;
        }
        long q = readLong();
        while(q--> 0)
        {
            long[] op = toLongArray();
            long b = op[0], c = op[1];
            long count = f[(int)b];
            sum = sum - b * count + c * count;
            f[(int)b] -= count;
            f[(int)c] += count;
            System.out.println(sum);
        }
    }

    int count(int k)
    {
        int sum = 0, cur = 0;
        while(sum + cur <= k)
        {
            sum += cur;
            cur++;
        }
        return cur - 1;
    }


    void c() throws Exception
    {
        long n = readLong();
        StringBuilder sb = new StringBuilder();
        String str = "";
        while(n > 0)
        {
            long rem = n % 26;
            if(rem == 0) rem = 26;
            n = (n - rem) / 26;
            str = (char)('a' + rem - 1) + str;
        }
        System.out.println(str);
    }

    int gcd(int a, int b)
    {
        if(b == 0) return a;
         return gcd(b, a % b);
    }

    void b() throws Exception
    {
        String s1 = in.readLine(),
                s2 = in.readLine();
        int n = s1.length();
        int ans = 0;
        for(int i = 0; i < n; i++)
        {
            char c1 = s1.charAt(i),
                c2 = s2.charAt(i);
            if(c1 != c2) ans++;
        }
        out.println(ans);
    }

    void a() throws Exception
    {
        int a = readInt();
        out.println(a + a * a + a * a * a);
    }
} Main static BufferedReader in; in static PrintWriter out = new PrintWriter(System.out); out new PrintWriter(System.out) static String file = "../in"; file "../in" static int test = 10; // 0 for local testing, 1 for std input test 10 static int inf = 1_000_000 inf 1_000_000 mod = 1_000_000_007; mod 1_000_000_007 void swap(int[]ary, int i, int j)
    {
        int t = ary[i];
        ary[i] = ary[j];
        ary[j] = t;
    } swap {
        int t = ary[i];
        ary[i] = ary[j];
        ary[j] = t;
    } int t = ary[i]; t ary[i] ary i ary[i] = ary[j] ary[i] ary i ary[j] ary j ary[j] = t ary[j] ary j t int[]ary ary int i i int j j String[] split() throws Exception
    {
        return in.readLine().split(" ");
    } split {
        return in.readLine().split(" ");
    } return in.readLine().split(" "); in.readLine().split(" ") in.readLine().split in.readLine() in.readLine in " " int readInt() throws Exception
    {
        return Integer.valueOf(in.readLine());
    } readInt {
        return Integer.valueOf(in.readLine());
    } return Integer.valueOf(in.readLine()); Integer.valueOf(in.readLine()) Integer.valueOf Integer in.readLine() in.readLine in long readLong() throws Exception
    {
        return Long.valueOf(in.readLine());
    } readLong {
        return Long.valueOf(in.readLine());
    } return Long.valueOf(in.readLine()); Long.valueOf(in.readLine()) Long.valueOf Long in.readLine() in.readLine in long[] toLongArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        long[] ary = new long[n];
        for(int i = 0; i < n; i++) ary[i] = Long.valueOf(sp[i]);
        return ary;
    } toLongArray {
        String[] sp = split();
        int n = sp.length;
        long[] ary = new long[n];
        for(int i = 0; i < n; i++) ary[i] = Long.valueOf(sp[i]);
        return ary;
    } String[] sp = split(); sp split() split int n = sp.length; n sp.length sp sp.length long[] ary = new long[n]; ary new long[n] n for(int i = 0; i < n; i++) ary[i] = Long.valueOf(sp[i]); int i = 0; int i = 0; i 0 i < n i n i++ i++ i ary[i] = Long.valueOf(sp[i]); ary[i] = Long.valueOf(sp[i]) ary[i] ary i Long.valueOf(sp[i]) Long.valueOf Long sp[i] sp i return ary; ary int[] toIntArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        int[] ary = new int[n];
        for(int i = 0; i < n; i++) ary[i] = Integer.valueOf(sp[i]);
        return ary;
    } toIntArray {
        String[] sp = split();
        int n = sp.length;
        int[] ary = new int[n];
        for(int i = 0; i < n; i++) ary[i] = Integer.valueOf(sp[i]);
        return ary;
    } String[] sp = split(); sp split() split int n = sp.length; n sp.length sp sp.length int[] ary = new int[n]; ary new int[n] n for(int i = 0; i < n; i++) ary[i] = Integer.valueOf(sp[i]); int i = 0; int i = 0; i 0 i < n i n i++ i++ i ary[i] = Integer.valueOf(sp[i]); ary[i] = Integer.valueOf(sp[i]) ary[i] ary i Integer.valueOf(sp[i]) Integer.valueOf Integer sp[i] sp i return ary; ary String reverse(String str)
    {
        return new StringBuilder(str).reverse().toString();
    } reverse {
        return new StringBuilder(str).reverse().toString();
    } return new StringBuilder(str).reverse().toString(); new StringBuilder(str).reverse().toString() new StringBuilder(str).reverse().toString new StringBuilder(str).reverse() new StringBuilder(str).reverse new StringBuilder(str) String str str long pow(long a, int pow)
    {
        long res = 1;
        while(pow > 0)
        {
            if(pow % 2 != 0) {
                res *= a;
                res %= mod;
            }
            a = a * a;
            a %= mod;
            pow /= 2;
        }

        return res;
    } pow {
        long res = 1;
        while(pow > 0)
        {
            if(pow % 2 != 0) {
                res *= a;
                res %= mod;
            }
            a = a * a;
            a %= mod;
            pow /= 2;
        }

        return res;
    } long res = 1; res 1 while(pow > 0)
        {
            if(pow % 2 != 0) {
                res *= a;
                res %= mod;
            }
            a = a * a;
            a %= mod;
            pow /= 2;
        } pow > 0 pow 0 {
            if(pow % 2 != 0) {
                res *= a;
                res %= mod;
            }
            a = a * a;
            a %= mod;
            pow /= 2;
        } if(pow % 2 != 0) {
                res *= a;
                res %= mod;
            } pow % 2 != 0 pow % 2 pow 2 0 {
                res *= a;
                res %= mod;
            } res *= a res a res %= mod res mod a = a * a a a * a a a a %= mod a mod pow /= 2 pow 2 return res; res long a a int pow pow public static void main(String[] args) throws Exception
    {
        int _k = Integer.valueOf("1");
        if(test > 0) in = new BufferedReader(new InputStreamReader(System.in));
        else in = new BufferedReader(new FileReader(file));
        if(test < 0) {String[] str = in.readLine().split(" ");
        char[] gg = in.readLine().toCharArray();}
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
        // System.out.println((-100 + 0) / 2);

        // char[] c = new char[4];
        // c[1] = '.';
        // for(char i = '0'; i <= '9'; i++)
        // {
        //     for(char j = '0'; j <= '9'; j++)
        //     {
        //         for(char k = '0'; k <= '9'; k++)
        //         {
        //             c[0] = i;
        //             c[2] = j;
        //             c[3] = k;
        //             double d = Double.valueOf(String.valueOf(c));
        //             int v = (int)(d * 100);
        //             String s1 = String.valueOf("" + c[0] + c[2] + c[3]),
        //                 s2 = String.valueOf(v);
        //             System.out.printf("%s %s %b\n", s1, s2, s1.equals(s2));
        //         }
        //     }
        // }


        new Main().b();
        out.flush();
    } main {
        int _k = Integer.valueOf("1");
        if(test > 0) in = new BufferedReader(new InputStreamReader(System.in));
        else in = new BufferedReader(new FileReader(file));
        if(test < 0) {String[] str = in.readLine().split(" ");
        char[] gg = in.readLine().toCharArray();}
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
        // System.out.println((-100 + 0) / 2);

        // char[] c = new char[4];
        // c[1] = '.';
        // for(char i = '0'; i <= '9'; i++)
        // {
        //     for(char j = '0'; j <= '9'; j++)
        //     {
        //         for(char k = '0'; k <= '9'; k++)
        //         {
        //             c[0] = i;
        //             c[2] = j;
        //             c[3] = k;
        //             double d = Double.valueOf(String.valueOf(c));
        //             int v = (int)(d * 100);
        //             String s1 = String.valueOf("" + c[0] + c[2] + c[3]),
        //                 s2 = String.valueOf(v);
        //             System.out.printf("%s %s %b\n", s1, s2, s1.equals(s2));
        //         }
        //     }
        // }


        new Main().b();
        out.flush();
    } int _k = Integer.valueOf("1"); _k Integer.valueOf("1") Integer.valueOf Integer "1" if(test > 0) in = new BufferedReader(new InputStreamReader(System.in));
        else in = new BufferedReader(new FileReader(file)); test > 0 test 0 in = new BufferedReader(new InputStreamReader(System.in)) in new BufferedReader(new InputStreamReader(System.in)) in = new BufferedReader(new FileReader(file)) in new BufferedReader(new FileReader(file)) if(test < 0) {String[] str = in.readLine().split(" ");
        char[] gg = in.readLine().toCharArray();} test < 0 test 0 {String[] str = in.readLine().split(" ");
        char[] gg = in.readLine().toCharArray();} String[] str = in.readLine().split(" "); str in.readLine().split(" ") in.readLine().split in.readLine() in.readLine in " " char[] gg = in.readLine().toCharArray(); gg in.readLine().toCharArray() in.readLine().toCharArray in.readLine() in.readLine in new Main().b() new Main().b new Main() out.flush() out.flush out String[] args args void f() throws Exception
    {
        int k = readInt();
        String s = in.readLine();
        int n = s.length();
        long prod = 1;
        int mod = 1_000_000_007;
        for(int i = 0; i < k; i++)
        {
            n++;
            prod = (prod * 26 * n) % mod;
        }
        System.out.println(prod);

    } f {
        int k = readInt();
        String s = in.readLine();
        int n = s.length();
        long prod = 1;
        int mod = 1_000_000_007;
        for(int i = 0; i < k; i++)
        {
            n++;
            prod = (prod * 26 * n) % mod;
        }
        System.out.println(prod);

    } int k = readInt(); k readInt() readInt String s = in.readLine(); s in.readLine() in.readLine in int n = s.length(); n s.length() s.length s long prod = 1; prod 1 int mod = 1_000_000_007; mod 1_000_000_007 for(int i = 0; i < k; i++)
        {
            n++;
            prod = (prod * 26 * n) % mod;
        } int i = 0; int i = 0; i 0 i < k i k i++ i++ i {
            n++;
            prod = (prod * 26 * n) % mod;
        } {
            n++;
            prod = (prod * 26 * n) % mod;
        } n++ n prod = (prod * 26 * n) % mod prod (prod * 26 * n) % mod (prod * 26 * n) prod * 26 * n prod 26 n mod System.out.println(prod) System.out.println System.out System System.out prod void e() throws Exception
    {
        int n = readInt();
        int[] ary = toIntArray();
        int xor = 0;
        for(int k : ary) xor ^= k;
        for(int i = 0; i < n; i++)
        {
            ary[i] ^= xor;
        }
        for(int k : ary) out.printf("%d ", k);
        
    } e {
        int n = readInt();
        int[] ary = toIntArray();
        int xor = 0;
        for(int k : ary) xor ^= k;
        for(int i = 0; i < n; i++)
        {
            ary[i] ^= xor;
        }
        for(int k : ary) out.printf("%d ", k);
        
    } int n = readInt(); n readInt() readInt int[] ary = toIntArray(); ary toIntArray() toIntArray int xor = 0; xor 0 for(int k : ary) xor ^= k; int k ary xor ^= k; xor ^= k xor k for(int i = 0; i < n; i++)
        {
            ary[i] ^= xor;
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            ary[i] ^= xor;
        } {
            ary[i] ^= xor;
        } ary[i] ^= xor ary[i] ary i xor for(int k : ary) out.printf("%d ", k); int k ary out.printf("%d ", k); out.printf("%d ", k) out.printf out "%d " k void d() throws Exception
    {
        long n = readLong();
        long[] ary = toLongArray();
        long[] f = new long[100010];
        long sum = 0;
        for(long k : ary)
        {
            f[(int)k]++;
            sum += k;
        }
        long q = readLong();
        while(q--> 0)
        {
            long[] op = toLongArray();
            long b = op[0], c = op[1];
            long count = f[(int)b];
            sum = sum - b * count + c * count;
            f[(int)b] -= count;
            f[(int)c] += count;
            System.out.println(sum);
        }
    } d {
        long n = readLong();
        long[] ary = toLongArray();
        long[] f = new long[100010];
        long sum = 0;
        for(long k : ary)
        {
            f[(int)k]++;
            sum += k;
        }
        long q = readLong();
        while(q--> 0)
        {
            long[] op = toLongArray();
            long b = op[0], c = op[1];
            long count = f[(int)b];
            sum = sum - b * count + c * count;
            f[(int)b] -= count;
            f[(int)c] += count;
            System.out.println(sum);
        }
    } long n = readLong(); n readLong() readLong long[] ary = toLongArray(); ary toLongArray() toLongArray long[] f = new long[100010]; f new long[100010] 100010 long sum = 0; sum 0 for(long k : ary)
        {
            f[(int)k]++;
            sum += k;
        } long k ary {
            f[(int)k]++;
            sum += k;
        } {
            f[(int)k]++;
            sum += k;
        } f[(int)k]++ f[(int)k] f (int)k sum += k sum k long q = readLong(); q readLong() readLong while(q--> 0)
        {
            long[] op = toLongArray();
            long b = op[0], c = op[1];
            long count = f[(int)b];
            sum = sum - b * count + c * count;
            f[(int)b] -= count;
            f[(int)c] += count;
            System.out.println(sum);
        } q--> 0 q-- q 0 {
            long[] op = toLongArray();
            long b = op[0], c = op[1];
            long count = f[(int)b];
            sum = sum - b * count + c * count;
            f[(int)b] -= count;
            f[(int)c] += count;
            System.out.println(sum);
        } long[] op = toLongArray(); op toLongArray() toLongArray long b = op[0] b op[0] op 0 c = op[1]; c op[1] op 1 long count = f[(int)b]; count f[(int)b] f (int)b sum = sum - b * count + c * count sum sum - b * count + c * count sum - b * count sum b * count b count c * count c count f[(int)b] -= count f[(int)b] f (int)b count f[(int)c] += count f[(int)c] f (int)c count System.out.println(sum) System.out.println System.out System System.out sum int count(int k)
    {
        int sum = 0, cur = 0;
        while(sum + cur <= k)
        {
            sum += cur;
            cur++;
        }
        return cur - 1;
    } count {
        int sum = 0, cur = 0;
        while(sum + cur <= k)
        {
            sum += cur;
            cur++;
        }
        return cur - 1;
    } int sum = 0 sum 0 cur = 0; cur 0 while(sum + cur <= k)
        {
            sum += cur;
            cur++;
        } sum + cur <= k sum + cur sum cur k {
            sum += cur;
            cur++;
        } sum += cur sum cur cur++ cur return cur - 1; cur - 1 cur 1 int k k void c() throws Exception
    {
        long n = readLong();
        StringBuilder sb = new StringBuilder();
        String str = "";
        while(n > 0)
        {
            long rem = n % 26;
            if(rem == 0) rem = 26;
            n = (n - rem) / 26;
            str = (char)('a' + rem - 1) + str;
        }
        System.out.println(str);
    } c {
        long n = readLong();
        StringBuilder sb = new StringBuilder();
        String str = "";
        while(n > 0)
        {
            long rem = n % 26;
            if(rem == 0) rem = 26;
            n = (n - rem) / 26;
            str = (char)('a' + rem - 1) + str;
        }
        System.out.println(str);
    } long n = readLong(); n readLong() readLong StringBuilder sb = new StringBuilder(); sb new StringBuilder() String str = ""; str "" while(n > 0)
        {
            long rem = n % 26;
            if(rem == 0) rem = 26;
            n = (n - rem) / 26;
            str = (char)('a' + rem - 1) + str;
        } n > 0 n 0 {
            long rem = n % 26;
            if(rem == 0) rem = 26;
            n = (n - rem) / 26;
            str = (char)('a' + rem - 1) + str;
        } long rem = n % 26; rem n % 26 n 26 if(rem == 0) rem = 26; rem == 0 rem 0 rem = 26 rem 26 n = (n - rem) / 26 n (n - rem) / 26 (n - rem) n rem 26 str = (char)('a' + rem - 1) + str str (char)('a' + rem - 1) + str (char)('a' + rem - 1) 'a' + rem 'a' rem 1 str System.out.println(str) System.out.println System.out System System.out str int gcd(int a, int b)
    {
        if(b == 0) return a;
         return gcd(b, a % b);
    } gcd {
        if(b == 0) return a;
         return gcd(b, a % b);
    } if(b == 0) return a; b == 0 b 0 return a; a return gcd(b, a % b); gcd(b, a % b) gcd b a % b a b int a a int b b void b() throws Exception
    {
        String s1 = in.readLine(),
                s2 = in.readLine();
        int n = s1.length();
        int ans = 0;
        for(int i = 0; i < n; i++)
        {
            char c1 = s1.charAt(i),
                c2 = s2.charAt(i);
            if(c1 != c2) ans++;
        }
        out.println(ans);
    } b {
        String s1 = in.readLine(),
                s2 = in.readLine();
        int n = s1.length();
        int ans = 0;
        for(int i = 0; i < n; i++)
        {
            char c1 = s1.charAt(i),
                c2 = s2.charAt(i);
            if(c1 != c2) ans++;
        }
        out.println(ans);
    } String s1 = in.readLine() s1 in.readLine() in.readLine in s2 = in.readLine(); s2 in.readLine() in.readLine in int n = s1.length(); n s1.length() s1.length s1 int ans = 0; ans 0 for(int i = 0; i < n; i++)
        {
            char c1 = s1.charAt(i),
                c2 = s2.charAt(i);
            if(c1 != c2) ans++;
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            char c1 = s1.charAt(i),
                c2 = s2.charAt(i);
            if(c1 != c2) ans++;
        } {
            char c1 = s1.charAt(i),
                c2 = s2.charAt(i);
            if(c1 != c2) ans++;
        } char c1 = s1.charAt(i) c1 s1.charAt(i) s1.charAt s1 i c2 = s2.charAt(i); c2 s2.charAt(i) s2.charAt s2 i if(c1 != c2) ans++; c1 != c2 c1 c2 ans++ ans out.println(ans) out.println out ans void a() throws Exception
    {
        int a = readInt();
        out.println(a + a * a + a * a * a);
    } a {
        int a = readInt();
        out.println(a + a * a + a * a * a);
    } int a = readInt(); a readInt() readInt out.println(a + a * a + a * a * a) out.println out a + a * a + a * a * a a + a * a + a * a * a a a * a a a a * a * a a * a * a a a a public class Main { 
  
    static BufferedReader in;
    static PrintWriter out = new PrintWriter(System.out);
    static String file = "../in";
    static int test = 10; // 0 for local testing, 1 for std input
    static int inf = 1_000_000, mod = 1_000_000_007;



    void swap(int[]ary, int i, int j)
    {
        int t = ary[i];
        ary[i] = ary[j];
        ary[j] = t;
    }
    
    String[] split() throws Exception
    {
        return in.readLine().split(" ");
    }

    int readInt() throws Exception
    {
        return Integer.valueOf(in.readLine());
    }

    long readLong() throws Exception
    {
        return Long.valueOf(in.readLine());
    }

    long[] toLongArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        long[] ary = new long[n];
        for(int i = 0; i < n; i++) ary[i] = Long.valueOf(sp[i]);
        return ary;
    }

    int[] toIntArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        int[] ary = new int[n];
        for(int i = 0; i < n; i++) ary[i] = Integer.valueOf(sp[i]);
        return ary;
    }

    String reverse(String str)
    {
        return new StringBuilder(str).reverse().toString();
    }


    long pow(long a, int pow)
    {
        long res = 1;
        while(pow > 0)
        {
            if(pow % 2 != 0) {
                res *= a;
                res %= mod;
            }
            a = a * a;
            a %= mod;
            pow /= 2;
        }

        return res;
    }

    public static void main(String[] args) throws Exception
    {
        int _k = Integer.valueOf("1");
        if(test > 0) in = new BufferedReader(new InputStreamReader(System.in));
        else in = new BufferedReader(new FileReader(file));
        if(test < 0) {String[] str = in.readLine().split(" ");
        char[] gg = in.readLine().toCharArray();}
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
        // System.out.println((-100 + 0) / 2);

        // char[] c = new char[4];
        // c[1] = '.';
        // for(char i = '0'; i <= '9'; i++)
        // {
        //     for(char j = '0'; j <= '9'; j++)
        //     {
        //         for(char k = '0'; k <= '9'; k++)
        //         {
        //             c[0] = i;
        //             c[2] = j;
        //             c[3] = k;
        //             double d = Double.valueOf(String.valueOf(c));
        //             int v = (int)(d * 100);
        //             String s1 = String.valueOf("" + c[0] + c[2] + c[3]),
        //                 s2 = String.valueOf(v);
        //             System.out.printf("%s %s %b\n", s1, s2, s1.equals(s2));
        //         }
        //     }
        // }


        new Main().b();
        out.flush();
    }
    void f() throws Exception
    {
        int k = readInt();
        String s = in.readLine();
        int n = s.length();
        long prod = 1;
        int mod = 1_000_000_007;
        for(int i = 0; i < k; i++)
        {
            n++;
            prod = (prod * 26 * n) % mod;
        }
        System.out.println(prod);

    }

    void e() throws Exception
    {
        int n = readInt();
        int[] ary = toIntArray();
        int xor = 0;
        for(int k : ary) xor ^= k;
        for(int i = 0; i < n; i++)
        {
            ary[i] ^= xor;
        }
        for(int k : ary) out.printf("%d ", k);
        
    }

    void d() throws Exception
    {
        long n = readLong();
        long[] ary = toLongArray();
        long[] f = new long[100010];
        long sum = 0;
        for(long k : ary)
        {
            f[(int)k]++;
            sum += k;
        }
        long q = readLong();
        while(q--> 0)
        {
            long[] op = toLongArray();
            long b = op[0], c = op[1];
            long count = f[(int)b];
            sum = sum - b * count + c * count;
            f[(int)b] -= count;
            f[(int)c] += count;
            System.out.println(sum);
        }
    }

    int count(int k)
    {
        int sum = 0, cur = 0;
        while(sum + cur <= k)
        {
            sum += cur;
            cur++;
        }
        return cur - 1;
    }


    void c() throws Exception
    {
        long n = readLong();
        StringBuilder sb = new StringBuilder();
        String str = "";
        while(n > 0)
        {
            long rem = n % 26;
            if(rem == 0) rem = 26;
            n = (n - rem) / 26;
            str = (char)('a' + rem - 1) + str;
        }
        System.out.println(str);
    }

    int gcd(int a, int b)
    {
        if(b == 0) return a;
         return gcd(b, a % b);
    }

    void b() throws Exception
    {
        String s1 = in.readLine(),
                s2 = in.readLine();
        int n = s1.length();
        int ans = 0;
        for(int i = 0; i < n; i++)
        {
            char c1 = s1.charAt(i),
                c2 = s2.charAt(i);
            if(c1 != c2) ans++;
        }
        out.println(ans);
    }

    void a() throws Exception
    {
        int a = readInt();
        out.println(a + a * a + a * a * a);
    }
} public class Main { 
  
    static BufferedReader in;
    static PrintWriter out = new PrintWriter(System.out);
    static String file = "../in";
    static int test = 10; // 0 for local testing, 1 for std input
    static int inf = 1_000_000, mod = 1_000_000_007;



    void swap(int[]ary, int i, int j)
    {
        int t = ary[i];
        ary[i] = ary[j];
        ary[j] = t;
    }
    
    String[] split() throws Exception
    {
        return in.readLine().split(" ");
    }

    int readInt() throws Exception
    {
        return Integer.valueOf(in.readLine());
    }

    long readLong() throws Exception
    {
        return Long.valueOf(in.readLine());
    }

    long[] toLongArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        long[] ary = new long[n];
        for(int i = 0; i < n; i++) ary[i] = Long.valueOf(sp[i]);
        return ary;
    }

    int[] toIntArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        int[] ary = new int[n];
        for(int i = 0; i < n; i++) ary[i] = Integer.valueOf(sp[i]);
        return ary;
    }

    String reverse(String str)
    {
        return new StringBuilder(str).reverse().toString();
    }


    long pow(long a, int pow)
    {
        long res = 1;
        while(pow > 0)
        {
            if(pow % 2 != 0) {
                res *= a;
                res %= mod;
            }
            a = a * a;
            a %= mod;
            pow /= 2;
        }

        return res;
    }

    public static void main(String[] args) throws Exception
    {
        int _k = Integer.valueOf("1");
        if(test > 0) in = new BufferedReader(new InputStreamReader(System.in));
        else in = new BufferedReader(new FileReader(file));
        if(test < 0) {String[] str = in.readLine().split(" ");
        char[] gg = in.readLine().toCharArray();}
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
        // System.out.println((-100 + 0) / 2);

        // char[] c = new char[4];
        // c[1] = '.';
        // for(char i = '0'; i <= '9'; i++)
        // {
        //     for(char j = '0'; j <= '9'; j++)
        //     {
        //         for(char k = '0'; k <= '9'; k++)
        //         {
        //             c[0] = i;
        //             c[2] = j;
        //             c[3] = k;
        //             double d = Double.valueOf(String.valueOf(c));
        //             int v = (int)(d * 100);
        //             String s1 = String.valueOf("" + c[0] + c[2] + c[3]),
        //                 s2 = String.valueOf(v);
        //             System.out.printf("%s %s %b\n", s1, s2, s1.equals(s2));
        //         }
        //     }
        // }


        new Main().b();
        out.flush();
    }
    void f() throws Exception
    {
        int k = readInt();
        String s = in.readLine();
        int n = s.length();
        long prod = 1;
        int mod = 1_000_000_007;
        for(int i = 0; i < k; i++)
        {
            n++;
            prod = (prod * 26 * n) % mod;
        }
        System.out.println(prod);

    }

    void e() throws Exception
    {
        int n = readInt();
        int[] ary = toIntArray();
        int xor = 0;
        for(int k : ary) xor ^= k;
        for(int i = 0; i < n; i++)
        {
            ary[i] ^= xor;
        }
        for(int k : ary) out.printf("%d ", k);
        
    }

    void d() throws Exception
    {
        long n = readLong();
        long[] ary = toLongArray();
        long[] f = new long[100010];
        long sum = 0;
        for(long k : ary)
        {
            f[(int)k]++;
            sum += k;
        }
        long q = readLong();
        while(q--> 0)
        {
            long[] op = toLongArray();
            long b = op[0], c = op[1];
            long count = f[(int)b];
            sum = sum - b * count + c * count;
            f[(int)b] -= count;
            f[(int)c] += count;
            System.out.println(sum);
        }
    }

    int count(int k)
    {
        int sum = 0, cur = 0;
        while(sum + cur <= k)
        {
            sum += cur;
            cur++;
        }
        return cur - 1;
    }


    void c() throws Exception
    {
        long n = readLong();
        StringBuilder sb = new StringBuilder();
        String str = "";
        while(n > 0)
        {
            long rem = n % 26;
            if(rem == 0) rem = 26;
            n = (n - rem) / 26;
            str = (char)('a' + rem - 1) + str;
        }
        System.out.println(str);
    }

    int gcd(int a, int b)
    {
        if(b == 0) return a;
         return gcd(b, a % b);
    }

    void b() throws Exception
    {
        String s1 = in.readLine(),
                s2 = in.readLine();
        int n = s1.length();
        int ans = 0;
        for(int i = 0; i < n; i++)
        {
            char c1 = s1.charAt(i),
                c2 = s2.charAt(i);
            if(c1 != c2) ans++;
        }
        out.println(ans);
    }

    void a() throws Exception
    {
        int a = readInt();
        out.println(a + a * a + a * a * a);
    }
} Main
import java.math.*;
import java.util.*;
import java.io.*;
  
public class Main { 
  
    static BufferedReader in;
    static PrintWriter out = new PrintWriter(System.out);
    static String file = "../in";
    static int test = 10; // 0 for local testing, 1 for std input
    static int inf = 1_000_000, mod = 1_000_000_007;



    void swap(int[]ary, int i, int j)
    {
        int t = ary[i];
        ary[i] = ary[j];
        ary[j] = t;
    }
    
    String[] split() throws Exception
    {
        return in.readLine().split(" ");
    }

    int readInt() throws Exception
    {
        return Integer.valueOf(in.readLine());
    }

    long readLong() throws Exception
    {
        return Long.valueOf(in.readLine());
    }

    long[] toLongArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        long[] ary = new long[n];
        for(int i = 0; i < n; i++) ary[i] = Long.valueOf(sp[i]);
        return ary;
    }

    int[] toIntArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        int[] ary = new int[n];
        for(int i = 0; i < n; i++) ary[i] = Integer.valueOf(sp[i]);
        return ary;
    }

    String reverse(String str)
    {
        return new StringBuilder(str).reverse().toString();
    }


    long pow(long a, int pow)
    {
        long res = 1;
        while(pow > 0)
        {
            if(pow % 2 != 0) {
                res *= a;
                res %= mod;
            }
            a = a * a;
            a %= mod;
            pow /= 2;
        }

        return res;
    }

    public static void main(String[] args) throws Exception
    {
        int _k = Integer.valueOf("1");
        if(test > 0) in = new BufferedReader(new InputStreamReader(System.in));
        else in = new BufferedReader(new FileReader(file));
        if(test < 0) {String[] str = in.readLine().split(" ");
        char[] gg = in.readLine().toCharArray();}
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
        // System.out.println((-100 + 0) / 2);

        // char[] c = new char[4];
        // c[1] = '.';
        // for(char i = '0'; i <= '9'; i++)
        // {
        //     for(char j = '0'; j <= '9'; j++)
        //     {
        //         for(char k = '0'; k <= '9'; k++)
        //         {
        //             c[0] = i;
        //             c[2] = j;
        //             c[3] = k;
        //             double d = Double.valueOf(String.valueOf(c));
        //             int v = (int)(d * 100);
        //             String s1 = String.valueOf("" + c[0] + c[2] + c[3]),
        //                 s2 = String.valueOf(v);
        //             System.out.printf("%s %s %b\n", s1, s2, s1.equals(s2));
        //         }
        //     }
        // }


        new Main().b();
        out.flush();
    }
    void f() throws Exception
    {
        int k = readInt();
        String s = in.readLine();
        int n = s.length();
        long prod = 1;
        int mod = 1_000_000_007;
        for(int i = 0; i < k; i++)
        {
            n++;
            prod = (prod * 26 * n) % mod;
        }
        System.out.println(prod);

    }

    void e() throws Exception
    {
        int n = readInt();
        int[] ary = toIntArray();
        int xor = 0;
        for(int k : ary) xor ^= k;
        for(int i = 0; i < n; i++)
        {
            ary[i] ^= xor;
        }
        for(int k : ary) out.printf("%d ", k);
        
    }

    void d() throws Exception
    {
        long n = readLong();
        long[] ary = toLongArray();
        long[] f = new long[100010];
        long sum = 0;
        for(long k : ary)
        {
            f[(int)k]++;
            sum += k;
        }
        long q = readLong();
        while(q--> 0)
        {
            long[] op = toLongArray();
            long b = op[0], c = op[1];
            long count = f[(int)b];
            sum = sum - b * count + c * count;
            f[(int)b] -= count;
            f[(int)c] += count;
            System.out.println(sum);
        }
    }

    int count(int k)
    {
        int sum = 0, cur = 0;
        while(sum + cur <= k)
        {
            sum += cur;
            cur++;
        }
        return cur - 1;
    }


    void c() throws Exception
    {
        long n = readLong();
        StringBuilder sb = new StringBuilder();
        String str = "";
        while(n > 0)
        {
            long rem = n % 26;
            if(rem == 0) rem = 26;
            n = (n - rem) / 26;
            str = (char)('a' + rem - 1) + str;
        }
        System.out.println(str);
    }

    int gcd(int a, int b)
    {
        if(b == 0) return a;
         return gcd(b, a % b);
    }

    void b() throws Exception
    {
        String s1 = in.readLine(),
                s2 = in.readLine();
        int n = s1.length();
        int ans = 0;
        for(int i = 0; i < n; i++)
        {
            char c1 = s1.charAt(i),
                c2 = s2.charAt(i);
            if(c1 != c2) ans++;
        }
        out.println(ans);
    }

    void a() throws Exception
    {
        int a = readInt();
        out.println(a + a * a + a * a * a);
    }
}