import java.util.Scanner;
import java.util.regex.Pattern;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] s = sc.nextLine().split("");
		String[] t = sc.nextLine().split("");
		sc.close();
		int size = s.length;
		int count = 0;
		for (int i = 0; i < size; i++) {
			if (!s[i].equals(t[i])) {
				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