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 Scala (judge verdict: Accepted)

object Main extends App {
  val src = io.Source.stdin.getLines.map(_.toInt).next

  def factorial(n: Int): Long = if (n == 0) 1 else n * factorial(n-1)

  println(factorial(src))
}