import java.util.*;
import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        String s = sc.nextLine();
        String t = sc.nextLine();
        
        int count = 0, i;
        for(i = 0; i < s.length(); i++){
            if(s.charAt(i) != t.charAt(i)) count++;
        }
        System.out.println(count);

    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz