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 AOJ
{
    class Factorial
    {
        static void Main(string[] args)
        {
            long result = 1;
            int num = int.Parse(System.Console.ReadLine());
            for(int i=1;i<=num;i++)
            {
                result = result * i;
            }
            System.Console.WriteLine(result);
        }
    }
}