import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
        char[] s = sc.next().toCharArray();
        char[] t = sc.next().toCharArray();

        int res=s.length;
        for(int i=0; i<s.length; i++){
            if(s[i] == t[i]){
                res--;
            }
        }
        System.out.println(res);
        }
    }
/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