
import java.util.*;
import java.io.*;
import java.math.*;

public class Main {

    static Scanner sc = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
    static PrintWriter out = new PrintWriter(System.out);

    public static void main(String[] args) throws Exception {

        String str = sc.next();
        String t = sc.next();

        if(str.equals(t))
            out.println("0");
        else {

            List<Character> hash1 = new ArrayList<>();
            //Set<Character> hash2 = new HashSet<>();

            for(int i = 0;i < str.length(); ++i){

                if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i));

            }


            out.println(hash1.size());
        }

        out.flush();
        out.close();
        sc.close();
    }

    static final int MOD = (int) 1e9 + 7;
    static final double PI = 3.14159265358979323846;

    // takes array input
    public static int[] init(int n) {

        int[] arr = new int[n];

        for (int i = 0; i < n; ++i)
            arr[i] = sc.nextInt();

        return arr;
    }

    // finds GCD of two number
    public static int gcd(int a, int b) {

        if (a == 0) {
            return b;
        }

        return gcd(b % a, a);
    }

    // checks whether a number is prime or not
    public static boolean prime(int n) {

        if (n < 2)
            return false;

        for (int i = 2; i * i <= n; ++i)
            if (n % i == 0)
                return false;

        return true;
    }
} import java.util.*; util.* java import java.io.*; io.* java import java.math.*; math.* java public class Main {

    static Scanner sc = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
    static PrintWriter out = new PrintWriter(System.out);

    public static void main(String[] args) throws Exception {

        String str = sc.next();
        String t = sc.next();

        if(str.equals(t))
            out.println("0");
        else {

            List<Character> hash1 = new ArrayList<>();
            //Set<Character> hash2 = new HashSet<>();

            for(int i = 0;i < str.length(); ++i){

                if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i));

            }


            out.println(hash1.size());
        }

        out.flush();
        out.close();
        sc.close();
    }

    static final int MOD = (int) 1e9 + 7;
    static final double PI = 3.14159265358979323846;

    // takes array input
    public static int[] init(int n) {

        int[] arr = new int[n];

        for (int i = 0; i < n; ++i)
            arr[i] = sc.nextInt();

        return arr;
    }

    // finds GCD of two number
    public static int gcd(int a, int b) {

        if (a == 0) {
            return b;
        }

        return gcd(b % a, a);
    }

    // checks whether a number is prime or not
    public static boolean prime(int n) {

        if (n < 2)
            return false;

        for (int i = 2; i * i <= n; ++i)
            if (n % i == 0)
                return false;

        return true;
    }
} Main static Scanner sc = new Scanner(new BufferedReader(new InputStreamReader(System.in))); sc new Scanner(new BufferedReader(new InputStreamReader(System.in))) static PrintWriter out = new PrintWriter(System.out); out new PrintWriter(System.out) static final int MOD = (int) 1e9 + 7; MOD (int) 1e9 + 7 (int) 1e9 7 static final double PI = 3.14159265358979323846; PI 3.14159265358979323846 public static void main(String[] args) throws Exception {

        String str = sc.next();
        String t = sc.next();

        if(str.equals(t))
            out.println("0");
        else {

            List<Character> hash1 = new ArrayList<>();
            //Set<Character> hash2 = new HashSet<>();

            for(int i = 0;i < str.length(); ++i){

                if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i));

            }


            out.println(hash1.size());
        }

        out.flush();
        out.close();
        sc.close();
    } main {

        String str = sc.next();
        String t = sc.next();

        if(str.equals(t))
            out.println("0");
        else {

            List<Character> hash1 = new ArrayList<>();
            //Set<Character> hash2 = new HashSet<>();

            for(int i = 0;i < str.length(); ++i){

                if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i));

            }


            out.println(hash1.size());
        }

        out.flush();
        out.close();
        sc.close();
    } String str = sc.next(); str sc.next() sc.next sc String t = sc.next(); t sc.next() sc.next sc if(str.equals(t))
            out.println("0");
        else {

            List<Character> hash1 = new ArrayList<>();
            //Set<Character> hash2 = new HashSet<>();

            for(int i = 0;i < str.length(); ++i){

                if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i));

            }


            out.println(hash1.size());
        } str.equals(t) str.equals str t out.println("0") out.println out "0" {

            List<Character> hash1 = new ArrayList<>();
            //Set<Character> hash2 = new HashSet<>();

            for(int i = 0;i < str.length(); ++i){

                if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i));

            }


            out.println(hash1.size());
        } List<Character> hash1 = new ArrayList<>(); hash1 new ArrayList<>() for(int i = 0;i < str.length(); ++i){

                if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i));

            } int i = 0; int i = 0; i 0 i < str.length() i str.length() str.length str ++i ++i i {

                if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i));

            } {

                if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i));

            } if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i)); str.charAt(i) != t.charAt(i) str.charAt(i) str.charAt str i t.charAt(i) t.charAt t i hash1.add(str.charAt(i)) hash1.add hash1 str.charAt(i) str.charAt str i out.println(hash1.size()) out.println out hash1.size() hash1.size hash1 out.flush() out.flush out out.close() out.close out sc.close() sc.close sc String[] args args // takes array input
    public static int[] init(int n) {

        int[] arr = new int[n];

        for (int i = 0; i < n; ++i)
            arr[i] = sc.nextInt();

        return arr;
    } init {

        int[] arr = new int[n];

        for (int i = 0; i < n; ++i)
            arr[i] = sc.nextInt();

        return arr;
    } int[] arr = new int[n]; arr new int[n] n for (int i = 0; i < n; ++i)
            arr[i] = sc.nextInt(); int i = 0; int i = 0; i 0 i < n i n ++i ++i i arr[i] = sc.nextInt(); arr[i] = sc.nextInt() arr[i] arr i sc.nextInt() sc.nextInt sc return arr; arr int n n // finds GCD of two number
    public static int gcd(int a, int b) {

        if (a == 0) {
            return b;
        }

        return gcd(b % a, a);
    } gcd {

        if (a == 0) {
            return b;
        }

        return gcd(b % a, a);
    } if (a == 0) {
            return b;
        } a == 0 a 0 {
            return b;
        } return b; b return gcd(b % a, a); gcd(b % a, a) gcd b % a b a a int a a int b b // checks whether a number is prime or not
    public static boolean prime(int n) {

        if (n < 2)
            return false;

        for (int i = 2; i * i <= n; ++i)
            if (n % i == 0)
                return false;

        return true;
    } prime {

        if (n < 2)
            return false;

        for (int i = 2; i * i <= n; ++i)
            if (n % i == 0)
                return false;

        return true;
    } if (n < 2)
            return false; n < 2 n 2 return false; false for (int i = 2; i * i <= n; ++i)
            if (n % i == 0)
                return false; int i = 2; int i = 2; i 2 i * i <= n i * i i i n ++i ++i i if (n % i == 0)
                return false; if (n % i == 0)
                return false; n % i == 0 n % i n i 0 return false; false return true; true int n n public class Main {

    static Scanner sc = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
    static PrintWriter out = new PrintWriter(System.out);

    public static void main(String[] args) throws Exception {

        String str = sc.next();
        String t = sc.next();

        if(str.equals(t))
            out.println("0");
        else {

            List<Character> hash1 = new ArrayList<>();
            //Set<Character> hash2 = new HashSet<>();

            for(int i = 0;i < str.length(); ++i){

                if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i));

            }


            out.println(hash1.size());
        }

        out.flush();
        out.close();
        sc.close();
    }

    static final int MOD = (int) 1e9 + 7;
    static final double PI = 3.14159265358979323846;

    // takes array input
    public static int[] init(int n) {

        int[] arr = new int[n];

        for (int i = 0; i < n; ++i)
            arr[i] = sc.nextInt();

        return arr;
    }

    // finds GCD of two number
    public static int gcd(int a, int b) {

        if (a == 0) {
            return b;
        }

        return gcd(b % a, a);
    }

    // checks whether a number is prime or not
    public static boolean prime(int n) {

        if (n < 2)
            return false;

        for (int i = 2; i * i <= n; ++i)
            if (n % i == 0)
                return false;

        return true;
    }
} public class Main {

    static Scanner sc = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
    static PrintWriter out = new PrintWriter(System.out);

    public static void main(String[] args) throws Exception {

        String str = sc.next();
        String t = sc.next();

        if(str.equals(t))
            out.println("0");
        else {

            List<Character> hash1 = new ArrayList<>();
            //Set<Character> hash2 = new HashSet<>();

            for(int i = 0;i < str.length(); ++i){

                if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i));

            }


            out.println(hash1.size());
        }

        out.flush();
        out.close();
        sc.close();
    }

    static final int MOD = (int) 1e9 + 7;
    static final double PI = 3.14159265358979323846;

    // takes array input
    public static int[] init(int n) {

        int[] arr = new int[n];

        for (int i = 0; i < n; ++i)
            arr[i] = sc.nextInt();

        return arr;
    }

    // finds GCD of two number
    public static int gcd(int a, int b) {

        if (a == 0) {
            return b;
        }

        return gcd(b % a, a);
    }

    // checks whether a number is prime or not
    public static boolean prime(int n) {

        if (n < 2)
            return false;

        for (int i = 2; i * i <= n; ++i)
            if (n % i == 0)
                return false;

        return true;
    }
} Main

import java.util.*;
import java.io.*;
import java.math.*;

public class Main {

    static Scanner sc = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
    static PrintWriter out = new PrintWriter(System.out);

    public static void main(String[] args) throws Exception {

        String str = sc.next();
        String t = sc.next();

        if(str.equals(t))
            out.println("0");
        else {

            List<Character> hash1 = new ArrayList<>();
            //Set<Character> hash2 = new HashSet<>();

            for(int i = 0;i < str.length(); ++i){

                if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i));

            }


            out.println(hash1.size());
        }

        out.flush();
        out.close();
        sc.close();
    }

    static final int MOD = (int) 1e9 + 7;
    static final double PI = 3.14159265358979323846;

    // takes array input
    public static int[] init(int n) {

        int[] arr = new int[n];

        for (int i = 0; i < n; ++i)
            arr[i] = sc.nextInt();

        return arr;
    }

    // finds GCD of two number
    public static int gcd(int a, int b) {

        if (a == 0) {
            return b;
        }

        return gcd(b % a, a);
    }

    // checks whether a number is prime or not
    public static boolean prime(int n) {

        if (n < 2)
            return false;

        for (int i = 2; i * i <= n; ++i)
            if (n % i == 0)
                return false;

        return true;
    }
}
