import java.math.BigDecimal;
import java.util.Scanner;

public class Main{
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        double d = scan.nextDouble();
        double v = (d/3)*(d/3)*(d/3);
        System.out.println(v);
    }
}
/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