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