Problem:
Factorial

Write a program which reads an integer n and prints the factorial of n. You can assume that n ≤ 20.

Input

An integer n (1 ≤ n ≤ 20) in a line.

Output

Print the factorial of n in a line.

Sample Input

5

Output for the Sample Input

120

Solution in C# (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Volume0019
{
    class Program
    {
        static void Main(string[] args)
        {
            long num = long.Parse(Console.ReadLine());
            long factorinal = Calclation.Factorial(num);
            Console.WriteLine(factorinal);
        }
    }
    class Calclation
    {
        internal static long Factorial(long num)
        {
            long factorinal = 1;
            for (int i = 1; i <= num; ++i)
            {
                factorinal *= i;
            }
            return factorinal;
        }
    }
}