# 循环嵌套初学者看过来！
#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
long long n,day,sum;
int main()
{
	cin >> n;
	for(int i = 1;i <= n;i++)
	{
		for(int j = 1;j <= i;j++)
		{
			day++;
			sum += i;
			if(day == n)
			{
				cout << sum;
				return 0;
			}
		}
	}
	return 0;
}