import java.util.*;

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

        Scanner sc = new Scanner(System.in);
        char[] a = sc.next().toCharArray();
        char[] b = sc.next().toCharArray();
        int n = a.length;
        int res = 0;
        for(int i=0; i<n; i++) {
            if(a[i] != b[i]) res++;
        }

        System.out.println(res);

    }

} import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {

        Scanner sc = new Scanner(System.in);
        char[] a = sc.next().toCharArray();
        char[] b = sc.next().toCharArray();
        int n = a.length;
        int res = 0;
        for(int i=0; i<n; i++) {
            if(a[i] != b[i]) res++;
        }

        System.out.println(res);

    }

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

        Scanner sc = new Scanner(System.in);
        char[] a = sc.next().toCharArray();
        char[] b = sc.next().toCharArray();
        int n = a.length;
        int res = 0;
        for(int i=0; i<n; i++) {
            if(a[i] != b[i]) res++;
        }

        System.out.println(res);

    } main {

        Scanner sc = new Scanner(System.in);
        char[] a = sc.next().toCharArray();
        char[] b = sc.next().toCharArray();
        int n = a.length;
        int res = 0;
        for(int i=0; i<n; i++) {
            if(a[i] != b[i]) res++;
        }

        System.out.println(res);

    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) char[] a = sc.next().toCharArray(); a sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc char[] b = sc.next().toCharArray(); b sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc int n = a.length; n a.length a a.length int res = 0; res 0 for(int i=0; i<n; i++) {
            if(a[i] != b[i]) res++;
        } int i=0; int i=0; i 0 i<n i n i++ i++ i {
            if(a[i] != b[i]) res++;
        } {
            if(a[i] != b[i]) res++;
        } if(a[i] != b[i]) res++; a[i] != b[i] a[i] a i b[i] b i res++ res System.out.println(res) System.out.println System.out System System.out res String[] args args public class Main {
    public static void main(String[] args) throws Exception {

        Scanner sc = new Scanner(System.in);
        char[] a = sc.next().toCharArray();
        char[] b = sc.next().toCharArray();
        int n = a.length;
        int res = 0;
        for(int i=0; i<n; i++) {
            if(a[i] != b[i]) res++;
        }

        System.out.println(res);

    }

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

        Scanner sc = new Scanner(System.in);
        char[] a = sc.next().toCharArray();
        char[] b = sc.next().toCharArray();
        int n = a.length;
        int res = 0;
        for(int i=0; i<n; i++) {
            if(a[i] != b[i]) res++;
        }

        System.out.println(res);

    }

} Main
import java.util.*;

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

        Scanner sc = new Scanner(System.in);
        char[] a = sc.next().toCharArray();
        char[] b = sc.next().toCharArray();
        int n = a.length;
        int res = 0;
        for(int i=0; i<n; i++) {
            if(a[i] != b[i]) res++;
        }

        System.out.println(res);

    }

}