import java.util.*;

class Main{
    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        int leng = scan.nextInt();
        scan.close();
        double result = 0.0;

        double amari = leng % 3;
        double qubeAmari = amari / 3;

        double qubeLength = leng - amari;
        qubeLength = qubeLength / 3;

        if(leng >= 3){result = (qubeLength + qubeAmari) * (qubeLength + qubeAmari) * (qubeLength + qubeAmari);}
        else {result = qubeAmari * qubeAmari * qubeAmari;}

        System.out.println(String.format("%.12f", result));
    }
}
/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