import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String a = sc.next(),b = sc.next();
        int count = 0;
        char[] A = a.toCharArray(),B = b.toCharArray();
        for (int i = 0; i <A.length ; i++) {
            if(A[i] == B[i])count++;
        }
        System.out.println(a.length() - count);

    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String a = sc.next(),b = sc.next();
        int count = 0;
        char[] A = a.toCharArray(),B = b.toCharArray();
        for (int i = 0; i <A.length ; i++) {
            if(A[i] == B[i])count++;
        }
        System.out.println(a.length() - count);

    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String a = sc.next(),b = sc.next();
        int count = 0;
        char[] A = a.toCharArray(),B = b.toCharArray();
        for (int i = 0; i <A.length ; i++) {
            if(A[i] == B[i])count++;
        }
        System.out.println(a.length() - count);

    } main {
        Scanner sc = new Scanner(System.in);
        String a = sc.next(),b = sc.next();
        int count = 0;
        char[] A = a.toCharArray(),B = b.toCharArray();
        for (int i = 0; i <A.length ; i++) {
            if(A[i] == B[i])count++;
        }
        System.out.println(a.length() - count);

    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String a = sc.next() a sc.next() sc.next sc b = sc.next(); b sc.next() sc.next sc int count = 0; count 0 char[] A = a.toCharArray() A a.toCharArray() a.toCharArray a B = b.toCharArray(); B b.toCharArray() b.toCharArray b for (int i = 0; i <A.length ; i++) {
            if(A[i] == B[i])count++;
        } int i = 0; int i = 0; i 0 i <A.length i A.length A A.length i++ i++ i {
            if(A[i] == B[i])count++;
        } {
            if(A[i] == B[i])count++;
        } if(A[i] == B[i])count++; A[i] == B[i] A[i] A i B[i] B i count++ count System.out.println(a.length() - count) System.out.println System.out System System.out a.length() - count a.length() a.length a count String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String a = sc.next(),b = sc.next();
        int count = 0;
        char[] A = a.toCharArray(),B = b.toCharArray();
        for (int i = 0; i <A.length ; i++) {
            if(A[i] == B[i])count++;
        }
        System.out.println(a.length() - count);

    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String a = sc.next(),b = sc.next();
        int count = 0;
        char[] A = a.toCharArray(),B = b.toCharArray();
        for (int i = 0; i <A.length ; i++) {
            if(A[i] == B[i])count++;
        }
        System.out.println(a.length() - count);

    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String a = sc.next(),b = sc.next();
        int count = 0;
        char[] A = a.toCharArray(),B = b.toCharArray();
        for (int i = 0; i <A.length ; i++) {
            if(A[i] == B[i])count++;
        }
        System.out.println(a.length() - count);

    }
}
