#include<bits/stdc++.h>

using namespace std;

int main() {
    int k, h = 0, t = 0;
    cin >> k;

    for (int i = 1;i<=10000; i++) {
        for (int j = 1; j <= i; j++) {
            h = h + i;
            t++;
            if (t == k) {
                cout << h << endl;
                break;
            }
        }
    }
    return 0;
}