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.Linq;

namespace Volume0_0019
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine
            (
                Enumerable
                    .Range(1, Convert.ToInt32(Console.ReadLine()))
                    .Select( i => (ulong)i )
                    .Aggregate((n, next) => n * next)
            );           
        }
    }
}