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 ConsoleApplication34
{
    class Program
    {
        static void Main()
        {
            int a = 1, s = int.Parse(Console.ReadLine());
            for(int b = 1; b <= s; b++)
            {
                a *= b;
            }
            Console.WriteLine(a);
        }
    }
}