#include <bits/stdc++.h>
using namespace std;

int main(){
    int k, day = 1, count = 0, coin = 0;
    cin >> k;
    while (count < k)
    {
        count += day;
        day++;
    }
    for (int i = 1; i <= day - 1; i++)
        coin += pow(i, 2);
    cout << coin - ((count - k) * (day - 1)) <<endl;
}