using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Nhap N;");

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

        int i=1;

        int tich=1;

        while(i<=N)

            {tich=tich*i;

            i++;

            }

    Console.WriteLine(tich);

    }

}