import java.util.*;

public class Main{

	public static void main(String[] args){

		Scanner sc = new Scanner(System.in);
        double N = sc.nextInt();
        double ans = N/3;
        System.out.println(Math.pow(ans,3));
      
	}

}



/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