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();
        sc.close();

        int count = 0;
        int idx = 0;
        for (char string : S.toCharArray()) {
            char x = T.charAt(idx);
            if (x != string) {
                count++;
            }
            idx++;
        }

        System.out.println(count);
    }
} 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();
        sc.close();

        int count = 0;
        int idx = 0;
        for (char string : S.toCharArray()) {
            char x = T.charAt(idx);
            if (x != string) {
                count++;
            }
            idx++;
        }

        System.out.println(count);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String S = sc.next();
        String T = sc.next();
        sc.close();

        int count = 0;
        int idx = 0;
        for (char string : S.toCharArray()) {
            char x = T.charAt(idx);
            if (x != string) {
                count++;
            }
            idx++;
        }

        System.out.println(count);
    } main {
        Scanner sc = new Scanner(System.in);
        String S = sc.next();
        String T = sc.next();
        sc.close();

        int count = 0;
        int idx = 0;
        for (char string : S.toCharArray()) {
            char x = T.charAt(idx);
            if (x != string) {
                count++;
            }
            idx++;
        }

        System.out.println(count);
    } 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 sc.close() sc.close sc int count = 0; count 0 int idx = 0; idx 0 for (char string : S.toCharArray()) {
            char x = T.charAt(idx);
            if (x != string) {
                count++;
            }
            idx++;
        } char string S.toCharArray() S.toCharArray S {
            char x = T.charAt(idx);
            if (x != string) {
                count++;
            }
            idx++;
        } {
            char x = T.charAt(idx);
            if (x != string) {
                count++;
            }
            idx++;
        } char x = T.charAt(idx); x T.charAt(idx) T.charAt T idx if (x != string) {
                count++;
            } x != string x string {
                count++;
            } count++ count idx++ idx System.out.println(count) System.out.println System.out System System.out count 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();
        sc.close();

        int count = 0;
        int idx = 0;
        for (char string : S.toCharArray()) {
            char x = T.charAt(idx);
            if (x != string) {
                count++;
            }
            idx++;
        }

        System.out.println(count);
    }
} public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String S = sc.next();
        String T = sc.next();
        sc.close();

        int count = 0;
        int idx = 0;
        for (char string : S.toCharArray()) {
            char x = T.charAt(idx);
            if (x != string) {
                count++;
            }
            idx++;
        }

        System.out.println(count);
    }
} 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();
        sc.close();

        int count = 0;
        int idx = 0;
        for (char string : S.toCharArray()) {
            char x = T.charAt(idx);
            if (x != string) {
                count++;
            }
            idx++;
        }

        System.out.println(count);
    }
}
