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

class Main{
public static void main(String args[]){
   Scanner sc = new Scanner(System.in);
   double L = sc.nextInt();
   double ret = Math.pow((L/3),3);
   System.out.println(BigDecimal.valueOf(ret).toPlainString());
}
  static boolean isPalindrome (String s) {
	int n = s.length();
	for (int i=0; i<n/2; i++) {
		if (s.charAt(i)!=s.charAt(n-i-1)) {return false;}
	}
	return true;
}
}

/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