import java.io.FileNotFoundException;
import java.util.Scanner;

public class Main {
    @SuppressWarnings("deprecation")
	public static void main(String[] args) throws FileNotFoundException {

//    	File file = new File("src/in.txt");

        //コード
//    	Scanner sc = new Scanner(file);
    	Scanner sc = new Scanner(System.in);

    	int L = sc.nextInt();

//    	BigDecimal POWL3 = new BigDecimal(L*L*L);
//
//    	BigDecimal ts = new BigDecimal(27);
//
//    	BigDecimal V = POWL3.di

    	int POWL3 = L*L*L;
    	double V = (double)POWL3/27;

    	System.out.println(String.format("%.8f", V));

    }

}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz