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

namespace contest19
{
    class Program
    {
        static void Main(string[] args)
        {
            var read_line_origin = Console.ReadLine();
//            string[] read_line = read_line_origin.Split();
            int n = int.Parse(read_line_origin);

            int ans = 1;

            for (int i = n; i > 0; i--)
            {
                ans *= i;
            }

            
            Console.WriteLine("{0}", ans);
            //            Console.ReadKey();
        }
    }
}