import java.util.*;
import java.math.*;

class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    double l = sc.nextDouble();
    BigDecimal  l2 = new BigDecimal(l/3);
    
    System.out.println(l2.multiply(l2).multiply(l2));
    
   
  }
}
/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