

import java.util.*;

public class Main {
public static void main(String[] args) {
		
		Scanner keyboard = new Scanner(System.in); 
		
		String S = keyboard.next();	
		String T = keyboard.next();	
		
		int Slong = S.length();
		
		int count = 0;
		for (int i=0; i<Slong; i++) {
			if(S.charAt(i) == T.charAt(i)) {
				
			}else {
				count++;
			}
		}
					
							
		System.out.println(count);
		keyboard.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