using System;

​

public class Program

{

    public static void Main()

    {

        int n, count = 1, a = 1;

        Console.WriteLine("enter n ");

        n = int.Parse(Console.ReadLine());

        while (count <= n)

        {

            a = a * count;

            count++;

        }

​

        if (n % 2 != 0)

            a = a * -1;

        Console.WriteLine("the number is " + a);

        {

        }

    }

}