import java.util.*;

class Main {

    static public double solve(int L) {
        return Math.pow(L/3.0, 3);
    }

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

        int L = sc.nextInt();

        sc.close();

        System.out.println(String.format("%.7f", solve(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