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>

int f(int a) {
	if (a == 1)
		return 1;
	return a*f(a - 1);
}

int main(void) {
	int n;
	scanf("%d", &n);
	printf("%d\n", f(n));
	while(1){}
	return 0;
}