import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);

		String S = scan.next();
		String T = scan.next();
		int ans = 0;

		String[] splitedS = S.split("");
		String[] splitedT = T.split("");

		for(int i = 0;i < S.length(); i++) {
			if(!(splitedS[i].equals(splitedT[i]))) {
				ans++;
			}
		}

		System.out.println(ans);

	}
}
/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