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;
namespace ConsoleApplication1{
    class Program{
        static void Main(string[] args) {
            long n = long.Parse(Console.ReadLine());
            for (int i = (int)n - 1; i >= 1; i--) {
                n *= i;
            }
            Console.WriteLine(n);
        }
    }
}