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 count = 0;
		
		for(int i=0;i<s.length();i++) {
			if(s.charAt(i) == t.charAt(i)) {
				continue;
			}else {
				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