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)

import scala.io.StdIn.readInt

object Main {
  def fact(n:Int,m:Long):Long = if(n==1) m else fact(n-1,m*n)

  def main(args:Array[String]) = println(fact(readInt,1))
}