#include <bits/stdc++.h>

using namespace std;

int main(){
	int k ;
	scanf("%d" , &k);
	int sum , n , day;
	for(int i = 1 ; i <= k;i++){
		if(day < k){
			day += i;
			n = i;
		}
	} 
	//cout<<day<<endl;
	//cout<<n<<endl;
	for(int i = 1 ; i <= n ; i++){
		sum += i * i;
		if(i == n){
			if(day - k == 0){
				//cout<<"1";
				//cout<<sum;
				sum = sum - i*i;
				sum += i * i;
			}else{
				//cout<<"0";
				//cout<<sum;
				sum = sum - i*i;
				sum += (n - day + k) * i;
			}
		}
	}
	printf("%d" , sum);
	return 0;

}