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: Time Limit Exceeded)

#include <stdio.h>
typedef long long int l;
l f(l n){if(n){return f(n-1)*n;}return 1;}
int main(void){l n;scanf("%d\n",&n);printf("%lld\n",f(n));return 0;}