import java.util.Scanner;


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

   
     System.out.println(s.length()-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