import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        Main m = new Main(sc);
        m.show(m.solve());
        sc.close();
    }
    
	//フィールド
    Scanner sc;
    double L;
    
    //入力
    Main(Scanner sc) {
        this.sc = sc;
        this.L = sc.nextDouble();
    }
    
    //解答処理
    private double solve() {
        double volume = Math.pow(L/3, 3);
        return volume;
    }
    
    //出力
    public void show(double answer) {
        System.out.printf("%.12f",answer);
    }

}
/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