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();
        // char[] ss = new char[s.length()];
        // char[] tt = new char[s.length()];
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            char si = s.charAt(i);
            char ti = t.charAt(i);
            if(si != ti){
                count++;
            }
        }
        System.out.println(count);
        sc.close();
    }
} 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();
        // char[] ss = new char[s.length()];
        // char[] tt = new char[s.length()];
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            char si = s.charAt(i);
            char ti = t.charAt(i);
            if(si != ti){
                count++;
            }
        }
        System.out.println(count);
        sc.close();
    }
} Main public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String t = sc.next();
        // char[] ss = new char[s.length()];
        // char[] tt = new char[s.length()];
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            char si = s.charAt(i);
            char ti = t.charAt(i);
            if(si != ti){
                count++;
            }
        }
        System.out.println(count);
        sc.close();
    } main {

        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String t = sc.next();
        // char[] ss = new char[s.length()];
        // char[] tt = new char[s.length()];
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            char si = s.charAt(i);
            char ti = t.charAt(i);
            if(si != ti){
                count++;
            }
        }
        System.out.println(count);
        sc.close();
    } 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 count = 0; count 0 for (int i = 0; i < s.length(); i++) {
            char si = s.charAt(i);
            char ti = t.charAt(i);
            if(si != ti){
                count++;
            }
        } int i = 0; int i = 0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
            char si = s.charAt(i);
            char ti = t.charAt(i);
            if(si != ti){
                count++;
            }
        } {
            char si = s.charAt(i);
            char ti = t.charAt(i);
            if(si != ti){
                count++;
            }
        } char si = s.charAt(i); si s.charAt(i) s.charAt s i char ti = t.charAt(i); ti t.charAt(i) t.charAt t i if(si != ti){
                count++;
            } si != ti si ti {
                count++;
            } count++ count System.out.println(count) System.out.println System.out System System.out count sc.close() sc.close sc 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();
        // char[] ss = new char[s.length()];
        // char[] tt = new char[s.length()];
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            char si = s.charAt(i);
            char ti = t.charAt(i);
            if(si != ti){
                count++;
            }
        }
        System.out.println(count);
        sc.close();
    }
} public class Main {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String t = sc.next();
        // char[] ss = new char[s.length()];
        // char[] tt = new char[s.length()];
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            char si = s.charAt(i);
            char ti = t.charAt(i);
            if(si != ti){
                count++;
            }
        }
        System.out.println(count);
        sc.close();
    }
} 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();
        // char[] ss = new char[s.length()];
        // char[] tt = new char[s.length()];
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            char si = s.charAt(i);
            char ti = t.charAt(i);
            if(si != ti){
                count++;
            }
        }
        System.out.println(count);
        sc.close();
    }
}