using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Please enter N= ");

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

        int i = 1;

        int output = 1;

        while (i <= n)

        {

            output = output * i;

            i++;

        }

        Console.WriteLine(output);

        Console.ReadLine();

    }

}