import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		String s = scanner.next();
		String t = scanner.next();
		int ans = solve(s.toCharArray(), t.toCharArray());
		System.out.println(ans);
	}

	public static int solve(char[] s, char[] t) {
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] != t[i]) {
				ans++;
			}
		}
		return 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