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 {
  def main(args: Array[String]) {
    val n = scala.io.StdIn.readLine.toInt
    println(func(n))
  }
  def func(n: Int): BigInt = {
    if(n == 0) 1 else n * func(n - 1)
  }
}