using namespace std;
long long n,sum,day,i,j;
int main()
{
	cin>>n;
	for(i=1;i<=n;i++)
	{
		sum = sum+i*i;
		day = (1+i)*i/2;
		if(day>=n)
		{
			sum=sum-(day-n)*i;
			cout<<sum;
			return 0;
		}
	}
}