#include<iostream>
using namespace std;
int main(){
	int k,sum=0,n=1;
	int i=1;
	cin>>k;
	for(;i<=k;){
		sum+=n*n;
		i=i+n;
		n++;
	}
	if((i-n+1<k)&&i>k){
		i=i-n+1;
		i=k-i;
		sum+=i*n;
	}
	cout<<sum;
	system("pause");
	return 0;
}
# 真的改不出来了，越改越错TAT