import java.lang.*;
import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    String s1 = scan.nextLine();
    String s2 = scan.nextLine();
    
   	int count = 0;
    
    if(!s1.equals(s2)){
      for(int i = 0; i < s1.length(); i++){
        if(s1.charAt(i) != s2.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