
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String S = sc.nextLine();
		String T = sc.nextLine();
		int s = S.length();
		int ans = 0;

	    for(int i = 0;i<S.length();i++) {
	    	if(!((S.charAt(i)==(T.charAt(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