import java.util.Scanner;

public class Factorial {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        int n;

        while (true) {

            System.out.print("请输入一个正整数（输入0退出循环）：");

            try {

                n = sc.nextInt();

            } catch (Exception e) {

                System.out.println("错误的类型！");

                sc.nextLine();

                continue;

            }

            if (n == 0) {

                break;

            }

            System.out.printf("%d! = %d\n", n, fact(n));

        }

        System.out.println("再见!");

    }

    private static long fact(int n) {

        if (n < 0) {

            System.out.println("错误的数值范围！");

            return -1;

        } else {

            return factorial(n);

        }

    }

    private static long factorial(int n) {

        if (n == 1) {

            return 1;

        } else {

            return n * factorial(--n);

        }

    }

}