import java.util.*;
import java.io.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		int num=0;
		String s=sc.nextLine(),t=sc.nextLine();

		for(int i=0;i<s.length();i++){
			if(s.charAt(i)!=t.charAt(i))num++;
		}
		System.out.print(num);
		sc.close();
	}
}

/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