import java.util.Scanner;

public class Main {
	public static void main(String args[]) {
		Scanner stdIn = new Scanner(System.in);
		char[] S = stdIn.next().toCharArray();
		char[] T = stdIn.next().toCharArray();
		
		int cnt = 0;
		
		for(int i = 0; i < S.length; i ++) {
			if(S[i] != T[i]) {
				cnt ++;
			}
		}
		
		System.out.println(cnt);
	}
}
/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