import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String s = input.next();
        String t = input.next();
        int ans = 0;
        for (int i = 0; i < s.length(); i++){
            if (s.charAt(i) != t.charAt(i)){
                ans += 1;
            }
        }
        System.out.println(ans);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String s = input.next();
        String t = input.next();
        int ans = 0;
        for (int i = 0; i < s.length(); i++){
            if (s.charAt(i) != t.charAt(i)){
                ans += 1;
            }
        }
        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String s = input.next();
        String t = input.next();
        int ans = 0;
        for (int i = 0; i < s.length(); i++){
            if (s.charAt(i) != t.charAt(i)){
                ans += 1;
            }
        }
        System.out.println(ans);
    } main {
        Scanner input = new Scanner(System.in);
        String s = input.next();
        String t = input.next();
        int ans = 0;
        for (int i = 0; i < s.length(); i++){
            if (s.charAt(i) != t.charAt(i)){
                ans += 1;
            }
        }
        System.out.println(ans);
    } Scanner input = new Scanner(System.in); input new Scanner(System.in) String s = input.next(); s input.next() input.next input String t = input.next(); t input.next() input.next input int ans = 0; ans 0 for (int i = 0; i < s.length(); i++){
            if (s.charAt(i) != t.charAt(i)){
                ans += 1;
            }
        } int i = 0; int i = 0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
            if (s.charAt(i) != t.charAt(i)){
                ans += 1;
            }
        } {
            if (s.charAt(i) != t.charAt(i)){
                ans += 1;
            }
        } if (s.charAt(i) != t.charAt(i)){
                ans += 1;
            } s.charAt(i) != t.charAt(i) s.charAt(i) s.charAt s i t.charAt(i) t.charAt t i {
                ans += 1;
            } ans += 1 ans 1 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 input = new Scanner(System.in);
        String s = input.next();
        String t = input.next();
        int ans = 0;
        for (int i = 0; i < s.length(); i++){
            if (s.charAt(i) != t.charAt(i)){
                ans += 1;
            }
        }
        System.out.println(ans);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String s = input.next();
        String t = input.next();
        int ans = 0;
        for (int i = 0; i < s.length(); i++){
            if (s.charAt(i) != t.charAt(i)){
                ans += 1;
            }
        }
        System.out.println(ans);
    }
} Main
import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String s = input.next();
        String t = input.next();
        int ans = 0;
        for (int i = 0; i < s.length(); i++){
            if (s.charAt(i) != t.charAt(i)){
                ans += 1;
            }
        }
        System.out.println(ans);
    }
}