#include <iostream>
#include "assert.h"

using namespace std;

#define L_MIN 3
#define L_MAX 1000000000

int main(){
	long long L;
	cin >> L;
	
	assert(L_MIN <= L);
	assert(L < L_MAX);
	assert(L%2 == 1);

	L = (L-1)/2;

	cout << L*L << endl;
}