package yukicoder;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {	
		long radrad =  new Scanner(System.in).nextLong()/3;
		long radius = 1;
		for(long i = 1 ; i*i < radrad ;i++){
			radius = radrad / i; 
		}
		System.out.println(radius);
	}

}