import java.util.*;
public class Main {
public static void main(String[] args){
	Scanner sc = new Scanner(System.in);
  	double L = sc.nextDouble();
  	L = L / 3;
  	System.out.println("" + L*L*L);
}
}

/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