import java.util.*;
public class Main {
        public static void main(String args[]){
          
        Scanner sc = new Scanner(System.in);
          
          //入力
          int L = sc.nextInt();
          
          double M = (double) L/3;
          
          //直方体の体積(最大)
          System.out.println(Math.pow(M,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