#include <cstdio>
#include <cmath>
using namespace std;

int main() {
	int k;
	scanf("%d", &k);
	int i = (sqrt(8 * k + 1) - 1) / 2;
	printf("%d", i*(i+1)*(2*i+1)/6+
		(k-i*(i+1)/2)*(i+1));
	return 0;
}