#include <bits/stdc++.h>
using namespace std;
int day,ans,fors,many;
int main(){
fors=0;
ans=1; 
cin>>day;
while(day<=0){
	fors=fors+ans*ans;
	day=day-ans;
	ans++;
}
if(day==0){
many=fors;
}
else{
	many=fors-((day-day-day)*ans);
}
cout<<many<<endl;
	return 0;
}