티끌 모아 태산

package Honeycomb;

import java.util.Scanner;

public class Main {

	public static boolean isIn(int sum, int n) {
		if (sum > n) {
			return false;
		} else
			return true;
	}

	public static void main(String args[]) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int sum = 1;
		int i;
		for (i = 1; isIn(sum, N); i++) {
			sum += (6 * i);
		}
		System.out.println(i);
	}
}