import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner stdIn = new Scanner(System.in);

        String s = stdIn.next();
        String t = stdIn.next();
        char[] s1 = new char[200000];
        char[] s2 = new char[200000];
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            s1[i] = s.charAt(i);
            s2[i] = t.charAt(i);
           if (s1[i] != s2[i]) {
               s1[i] = s2[i];
               count++;
           }
        }
        System.out.println(count);
    }
} import java.util.Scanner; Scanner java.util class Main {
    public static void main(String[] args) {
        Scanner stdIn = new Scanner(System.in);

        String s = stdIn.next();
        String t = stdIn.next();
        char[] s1 = new char[200000];
        char[] s2 = new char[200000];
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            s1[i] = s.charAt(i);
            s2[i] = t.charAt(i);
           if (s1[i] != s2[i]) {
               s1[i] = s2[i];
               count++;
           }
        }
        System.out.println(count);
    }
} Main public static void main(String[] args) {
        Scanner stdIn = new Scanner(System.in);

        String s = stdIn.next();
        String t = stdIn.next();
        char[] s1 = new char[200000];
        char[] s2 = new char[200000];
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            s1[i] = s.charAt(i);
            s2[i] = t.charAt(i);
           if (s1[i] != s2[i]) {
               s1[i] = s2[i];
               count++;
           }
        }
        System.out.println(count);
    } main {
        Scanner stdIn = new Scanner(System.in);

        String s = stdIn.next();
        String t = stdIn.next();
        char[] s1 = new char[200000];
        char[] s2 = new char[200000];
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            s1[i] = s.charAt(i);
            s2[i] = t.charAt(i);
           if (s1[i] != s2[i]) {
               s1[i] = s2[i];
               count++;
           }
        }
        System.out.println(count);
    } Scanner stdIn = new Scanner(System.in); stdIn new Scanner(System.in) String s = stdIn.next(); s stdIn.next() stdIn.next stdIn String t = stdIn.next(); t stdIn.next() stdIn.next stdIn char[] s1 = new char[200000]; s1 new char[200000] 200000 char[] s2 = new char[200000]; s2 new char[200000] 200000 int count = 0; count 0 for (int i = 0; i < s.length(); i++) {
            s1[i] = s.charAt(i);
            s2[i] = t.charAt(i);
           if (s1[i] != s2[i]) {
               s1[i] = s2[i];
               count++;
           }
        } int i = 0; int i = 0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
            s1[i] = s.charAt(i);
            s2[i] = t.charAt(i);
           if (s1[i] != s2[i]) {
               s1[i] = s2[i];
               count++;
           }
        } {
            s1[i] = s.charAt(i);
            s2[i] = t.charAt(i);
           if (s1[i] != s2[i]) {
               s1[i] = s2[i];
               count++;
           }
        } s1[i] = s.charAt(i) s1[i] s1 i s.charAt(i) s.charAt s i s2[i] = t.charAt(i) s2[i] s2 i t.charAt(i) t.charAt t i if (s1[i] != s2[i]) {
               s1[i] = s2[i];
               count++;
           } s1[i] != s2[i] s1[i] s1 i s2[i] s2 i {
               s1[i] = s2[i];
               count++;
           } s1[i] = s2[i] s1[i] s1 i s2[i] s2 i count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args
import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner stdIn = new Scanner(System.in);

        String s = stdIn.next();
        String t = stdIn.next();
        char[] s1 = new char[200000];
        char[] s2 = new char[200000];
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            s1[i] = s.charAt(i);
            s2[i] = t.charAt(i);
           if (s1[i] != s2[i]) {
               s1[i] = s2[i];
               count++;
           }
        }
        System.out.println(count);
    }
}