import java.util.*;

public class Main{
public static void main(String[]args){
    double a = 0.0;
    Scanner sc = new Scanner(System.in);
    a = sc.nextInt();
    double count =0.0;
    count=a*a*a/27.0;
    System.out.println(count);
}

}
/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