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;

class AOJ{
  static void Main(string[] args)
  {
    long ans = 1;
    string s;

    s = Console.ReadLine();

    for (int i = 1; i <= int.Parse(s); i++)
      ans *= i;

    Console.WriteLine(ans);
  }
}