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: Wrong Answer)

using System;
using System.Linq;

namespace AOJ
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            Console.WriteLine(
                Enumerable.Range(1, n).Aggregate((a, b) => a * b));
        }
    }
}