#include<stdio.h>

int main()
{
	int n = 0;
	int res = 1;


	printf("n:");
	scanf("%i",&n);


	if(n % 2 == 0)
	{
		while(n > 0)
		{
			res = res * n;
			n = n - 2;
		}
	}
	else
	{
		while(n > 0)
		{
			res = res * n;
			n = n - 2;
		}
	}


	printf("res = %i",res);
	return 0;
}