#include <stdio.h>
int del(int k)
{
	int x=1;
	int sum=0;
	while(k!=0)
	{
	if(k>x)
		sum+=x*x;
		k=k-x;
		x++;
		if(k<=x)
		{
		sum+=k*x;
		return sum;}
		}
}
int main()
{
	int k;
	scanf("%d",&k);
	printf("%d",del(k));
	return 0;
}