

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {

	public static void main(String[] args) throws Exception {
	BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
	String s=br.readLine().trim();
	String t=br.readLine().trim();
	algo(s,t);	
	
	}

	public static void algo(String s,String t) {
		int res=0;
		for(int i=0;i<s.length();i++) {
			char c1=s.charAt(i);
			char c2=t.charAt(i);
			if(c1!=c2) {
				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