import java.util.*;
import java.math.*;

public class Main {

  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    double l = sc.nextDouble();

    double x = l/3;
    double y = l/3;
    double z = l-x-y;

    System.out.println(x*y*z);

  }

}

/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