백준 2292번(Java)

import java.io.*;

public class Main {

	public static void main(String[] args) throws NumberFormatException, IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

		int N = Integer.parseInt(br.readLine());
		int result = 1;
		int range = 2;

		if(N == 1) {
			result = 1;
		}
		else {
			while(range <= N) {
				range = range + (6 * result);
				result++;
			}
		}
		bw.write(String.valueOf(result));

		br.close();
		bw.flush();
		bw.close();
	}
}