include<bits/stdc++.h>

using namespace std; int main() {

int sum=0;
double n;
cin>>n;
if(sqrt(1+8*n)==1.0*int(sqrt(1+8*n))) {
	int k=(sqrt(1+8*n)-1)/2;
	cout<<(k*(k+1)*(2*k+1))/6;
}
if(sqrt(1+8*n)!=1.0*int(sqrt(1+8*n))) {
	int k=(sqrt(1+8*n)-1)/2;
	sum+=(k*(k+1)*(2*k+1))/6;
	sum+=(n-(k*(k+1)/2))*(k+1);
	cout<<sum;
}
return 0;

}