import java.util.Scanner;

public class Main {
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String t = sc.next();
        
        String ss[] = s.split("");
        String ts[] = t.split("");
        
        int ans = 0;
        for(int i = 0; i < s.length();i++){
            if(!ss[i].equals(ts[i])){
                ans++;
            }
        }
        
        System.out.println(ans);
    }
} import java.util.Scanner; Scanner 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();
        
        String ss[] = s.split("");
        String ts[] = t.split("");
        
        int ans = 0;
        for(int i = 0; i < s.length();i++){
            if(!ss[i].equals(ts[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();
        
        String ss[] = s.split("");
        String ts[] = t.split("");
        
        int ans = 0;
        for(int i = 0; i < s.length();i++){
            if(!ss[i].equals(ts[i])){
                ans++;
            }
        }
        
        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String t = sc.next();
        
        String ss[] = s.split("");
        String ts[] = t.split("");
        
        int ans = 0;
        for(int i = 0; i < s.length();i++){
            if(!ss[i].equals(ts[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 String ss[] = s.split(""); ss s.split("") s.split s "" String ts[] = t.split(""); ts t.split("") t.split t "" int ans = 0; ans 0 for(int i = 0; i < s.length();i++){
            if(!ss[i].equals(ts[i])){
                ans++;
            }
        } int i = 0; int i = 0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
            if(!ss[i].equals(ts[i])){
                ans++;
            }
        } {
            if(!ss[i].equals(ts[i])){
                ans++;
            }
        } if(!ss[i].equals(ts[i])){
                ans++;
            } !ss[i].equals(ts[i]) ss[i].equals(ts[i]) ss[i].equals ss[i] ss i ts[i] ts 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();
        
        String ss[] = s.split("");
        String ts[] = t.split("");
        
        int ans = 0;
        for(int i = 0; i < s.length();i++){
            if(!ss[i].equals(ts[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();
        
        String ss[] = s.split("");
        String ts[] = t.split("");
        
        int ans = 0;
        for(int i = 0; i < s.length();i++){
            if(!ss[i].equals(ts[i])){
                ans++;
            }
        }
        
        System.out.println(ans);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String t = sc.next();
        
        String ss[] = s.split("");
        String ts[] = t.split("");
        
        int ans = 0;
        for(int i = 0; i < s.length();i++){
            if(!ss[i].equals(ts[i])){
                ans++;
            }
        }
        
        System.out.println(ans);
    }
}
