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;

namespace mondai0019
{
	class Program
	{
		static void Main(string[] args)
		{
			var	n	= long.Parse( Console.ReadLine() );
			
			long	a	= 1;
			for( int i = 1; i <= n; i++ ) {
				a	*= i;
			}
			Console.WriteLine( a );
		}
	}
}