import java.util.Scanner;
import java.util.Arrays;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int ans = 0;
    char[] s = sc.nextLine().toCharArray();
    char[] t = sc.nextLine().toCharArray();
    for (int cnt = 0; cnt < s.length; cnt++) {
      if (s[cnt] != t[cnt]) {
        ans++;
      }
    }
    System.out.println(ans);
    sc.close();
  }
}
/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