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

public class Main{

    public static void main(String args[]){
       Scanner sc = new Scanner(System.in);
		BigDecimal l = new BigDecimal(sc.nextLine());
		BigDecimal three = new BigDecimal("3");
		//DecimalFormat df = new decimalFormat("0.000000000000"):
		BigDecimal res = l.divide(three, 12, RoundingMode.HALF_UP).pow(3);
		
		System.out.println(res);
    }
	
	public static boolean isKai(String s){
		return s.equals(new StringBuilder(s).reverse().toString());
	}
}



/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