import java.io.IOException;
import java.util.Scanner;

public class Main {

public static void main(String[] args) throws IOException {
		Scanner scan = new Scanner(System.in);
		String s = scan.next();
  		String t = scan.next();
  	int cnt = 0;
  		for(int i=0; i<s.length(); i++){
          if(s.charAt(i) != t.charAt(i)){
            cnt++;
          }
          
        }
  
		System.out.println(cnt);
}
}

/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