using System;

public class Program

{

    public static void Main()

    {

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

        int result = Factorial(userInput);

        Console.WriteLine(result);

    }

    static int Factorial(int number)

    {

        if (number < 0)

        {

            Console.WriteLine("Cannot calculate factorial for negative numbers.");

            return -1; 

        }

        if (number == 0 || number == 1)

        {

            return 1;

        }

        int result = 1;

        for (int i = 2; i <= number; i++)

        {

            result *= i;

        }

        return result;

    }

}