python/TangDou/CSP-J/AcWingTraining/T4/461.cpp

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

int main() {
    int n;
    cin >> n;

    int res = 0;
    for (int i = 1, k = 0; k < n; i++)
        for (int j = 0; j < i && k < n; j++, k++)
            res += i;

    cout << res << endl;
    return 0;
}