[NOIP2015]金币

#include <iostream>
using namespace std;

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

    int sum = 0;
    int state = 1;
    int dayCount = 0; // Counter to track the number of days at the current state

    for (int i = 1; i <= k; i++) {
        sum += state;
        dayCount++;

        // When dayCount equals state, reset dayCount and increment state
        if (dayCount == state) {
            dayCount = 0;
            state++;
        }
    }

    cout << sum << endl;
    return 0;
}