240412 벌집

public static void main(String[] args) throws IOException {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

	int n = Integer.parseInt(br.readLine());
	int count = 1;
	int range = 2;

	if (n == 1) {
		System.out.println(1);
	} else {
		while (range <= n) {
			range = range + (6 * count);
			count++;
		}
		System.out.println(count);
	}
}

출처:https://www.acmicpc.net/problem/2292