#include <iostream>
using namespace std;
int giam(int n)
{
	int tongn = 0;
	for (int i = n; i >= 1; i--)
	{
		tongn = tongn + i;
	}
	return tongn;
}
int main()
{
	int n, tong = 0;
	cout << "Nhap n: ";
	cin >> n;
	for (int i = 0; i <= n; i++)
	{
		tong = tong + giam(i);
	}
	cout << "Dap so la: " << tong;
}