import java.util.Scanner;
import java.math.BigDecimal;
class Main{
public static void main(String[] args){
Scanner scan = new Scanner(System.in);

  double L = scan.nextInt();
    double M = L / 3;
  BigDecimal bd1 = new BigDecimal(M);
  BigDecimal bd2 = new BigDecimal(M);
  BigDecimal result1 = bd1.multiply(bd2);
  BigDecimal result2 = result1.multiply(bd1);
  
  System.out.println(result2);
  
 }
}
/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