import java.util.*;
 
public class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		String n = sc.next();
      	String s = sc.next();
      	int count = 0;
      	for(int cnt = 0;cnt < n.length();cnt++){
        	if(n.charAt(cnt) != s.charAt(cnt)){
            	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