import java.util.Scanner;

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

    S = sc.next();
    T = sc.next();
    for (int i = 0; i < S.length(); i++) {
      if (S.charAt(i) != T.charAt(i)) {
        cnt++;
      }
    }
    System.out.print(cnt);
  }
}
/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