import java.util.*;

import javax.lang.model.util.ElementScanner6;
 
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		int count = 0;

		for(int i = 0; i < S.length(); i ++){
			char s = S.charAt(i);
			char t = T.charAt(i);
			if(s != t)
			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