#include<bits/stdc++.h>
using namespace std;
int main(){
	int k;
	cin >> k;
	int coin = 0;
	int zts = 0, flag = 0;
	for(int shouru = 1;flag == 0;shouru++){
		for(int day = 1; day <= shouru; ++day){
			coin += shouru;
			++zts;
			if(zts == k){
				flag = 1;
				break;
			}
		}
	}
	cout << coin;
	return 0;
}