40pts求调，玄关

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll k,s,l;
signed main(){
	cin>>k;
	for(int i=1;(1+i)*i/2<=k;i++)
		l=i;
	cout<<l*(l+1)*(2*l+1)/6;
	return 0;
}