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 JavaScript (judge verdict: Accepted)

function fact(x){
   if(x==0){return 1;}
   return x * fact(x-1);}
var input = require('fs').readFileSync('/dev/stdin', 'utf8');
console.log(fact(input));