import java.math.BigInteger;
import java.util.*;
import java.io.*;

public class Main {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int L = in.nextInt();
      	double side = (double) L / 3;
        System.out.println(side * side * side);
    }
}
/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