import java.util.*;
import java.io.*;
import java.lang.*;
public class Main {

	public static void main(String[] args) throws Exception{
		// TODO Auto-generated method stub
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		String s1=br.readLine().trim();
		String s2=br.readLine().trim();
		int count=0;
		for(int i=0;i<s1.length();i++)
			if(s1.charAt(i)!=s2.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