import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner c = new Scanner(System.in);

        String str1 = c.nextLine();
        String str2 = c.nextLine();
        int count = 0;

        for (int i = 0; i < str1.length(); i++) {
            if (!str1.substring(i, i + 1).equals(str2.substring(i, i + 1))) {
                count++;
            }
        }

        System.out.println(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