import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        String S = in.nextLine();
        String T = in.nextLine();
      int A = 0;

for (int count = 0; count < S.length(); count++){
 if(S.charAt(count) == T.charAt(count)){
  A = A +1 ;
 }
}

System.out.println(S.length()-A);
        }
    }
/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