import java.util.*;
import java.math.BigDecimal;
public class Main{
  public static void main(String[] args){
    Scanner sc =new Scanner(System.in);
    int L=sc.nextInt();
    if(L==1){System.out.println(0.0370370);}
    else if(L==2){System.out.println(0.0740740);}else{
    int M=L*L*L;
    double m=M/27;
    String X = BigDecimal.valueOf(m).toPlainString();
    System.out.println(X);}
  }
}

/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