#include<iostream>
#include<cmath>
using namespace std;
int main()
{

	int M,N=1,sum=1,count=0,i;
	cin>>M;
	while(sum<M)
	{
		N++;
		sum+=N;
	}
	for(i=1;i<=N;i++)
	{
		if(i<N)
		count+=pow(i,2);
		else
		count+=(N-(sum-M))*N;
	}
	cout<<count;
	return 0;
}