import java.util.Scanner;

public class Main {
  public static void main(String[] args){
      Scanner sc = new Scanner(System.in);
      // 文字列の入力1
      String str1 = sc.nextLine();
      // 文字列の入力1
      String str2 = sc.nextLine();
      if(!str1.equals(str2)) {
        int count = 0;
        for(int i = 0;i<str1.length();i++) {
          if(str1.charAt(i)!= str2.charAt(i)) {
            count++;
          }
        }
        System.out.println(count);
      }else {
        System.out.println(0);
      }
  }
}
/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