#include<bits/stdc++.h>
using namespace std;
int main()
{
	int k,n=0,i=0,sum=0;
	cin>>k;
	while(i<k)
	{
		n++;
		sum+=n*n;
		i+=n;
	}
	if(i==k)
		cout<<sum;
	else
		cout<<sum-(i-k)*n;
	return 0;
}