import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

import static java.lang.System.in;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        long n = Long.parseLong(reader.readLine());
        System.out.println((int)Math.sqrt(n/3));
    }
}