#include<bits/stdc++.h>
using namespace std;
int main(){
	long long sum1=0,sum2=0,t=0;
	int i,j,k;
	cin>>k;
	for(i=0;i<k;i++){
		sum1+=i;
		if(sum1<=k&&(sum1+i)>k)break;
	} 
	for(j=0;j<=i;j++){
		sum2+=j*j;
	}
	cout<<sum2+(k-sum1)*(i+1)<<endl;
	return 0;
}