
import java.util.Scanner;

public class Main {
   public static void main(String[] args) {
       Scanner s= new Scanner(System.in);
       String st = s.nextLine();
       String t = s.nextLine();
       int count = 0, len =st.length();
       for(int i = 0;i < len; ++i) {
           if(st.charAt(i)!=t.charAt(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