import java.util.*;

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

        String S = sc.next();
        String T = sc.next();
        int N = S.length();
        
        int ans = 0;
        for (int i = 0; i < N; i++) {
            if (S.charAt(i) != T.charAt(i)) {
                ans++;
            }
        }
        System.out.println(ans);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        String S = sc.next();
        String T = sc.next();
        int N = S.length();
        
        int ans = 0;
        for (int i = 0; i < N; i++) {
            if (S.charAt(i) != T.charAt(i)) {
                ans++;
            }
        }
        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        String S = sc.next();
        String T = sc.next();
        int N = S.length();
        
        int ans = 0;
        for (int i = 0; i < N; i++) {
            if (S.charAt(i) != T.charAt(i)) {
                ans++;
            }
        }
        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);

        String S = sc.next();
        String T = sc.next();
        int N = S.length();
        
        int ans = 0;
        for (int i = 0; i < N; i++) {
            if (S.charAt(i) != T.charAt(i)) {
                ans++;
            }
        }
        System.out.println(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String S = sc.next(); S sc.next() sc.next sc String T = sc.next(); T sc.next() sc.next sc int N = S.length(); N S.length() S.length S int ans = 0; ans 0 for (int i = 0; i < N; i++) {
            if (S.charAt(i) != T.charAt(i)) {
                ans++;
            }
        } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
            if (S.charAt(i) != T.charAt(i)) {
                ans++;
            }
        } {
            if (S.charAt(i) != T.charAt(i)) {
                ans++;
            }
        } if (S.charAt(i) != T.charAt(i)) {
                ans++;
            } S.charAt(i) != T.charAt(i) S.charAt(i) S.charAt S i T.charAt(i) T.charAt T i {
                ans++;
            } ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        String S = sc.next();
        String T = sc.next();
        int N = S.length();
        
        int ans = 0;
        for (int i = 0; i < N; i++) {
            if (S.charAt(i) != T.charAt(i)) {
                ans++;
            }
        }
        System.out.println(ans);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        String S = sc.next();
        String T = sc.next();
        int N = S.length();
        
        int ans = 0;
        for (int i = 0; i < N; i++) {
            if (S.charAt(i) != T.charAt(i)) {
                ans++;
            }
        }
        System.out.println(ans);
    }
} Main
import java.util.*;

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

        String S = sc.next();
        String T = sc.next();
        int N = S.length();
        
        int ans = 0;
        for (int i = 0; i < N; i++) {
            if (S.charAt(i) != T.charAt(i)) {
                ans++;
            }
        }
        System.out.println(ans);
    }
}
