using System;

public class Program

{

    public static void Main()

    {

         Console.WriteLine("n:");

 int  n=Convert.ToInt32(Console.ReadLine());

          int sum=n;

  var k=n;

  for (var i = 1; i < k; i++) {

    n=n-1;

    sum=sum*n;

  }

​

        Console.WriteLine(sum);

    }

}