import java.io.*;

public class Main {

  static boolean checkKaibun(String str){
    StringBuilder t = new StringBuilder(str);
    return (str.equals(t.reverse().toString()));
  }

  public static void main(String[] args) throws IOException {

    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    
    String[] in;
    in = br.readLine().split(" ");
    double l = Double.parseDouble(in[0]);

    br.close();

    System.out.println(String.format("%.10f", (l / 3.0) * (l / 3.0) * (l / 3.0)));
    
  }
}
/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