import java.math.BigDecimal;
import java.math.MathContext;
import java.math.RoundingMode;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		BigDecimal L = new BigDecimal(sc.nextLine());
		BigDecimal div = new BigDecimal(3.0);
		MathContext mc = new MathContext(10,RoundingMode.HALF_UP);
		BigDecimal cutNum = L.divide(div, mc);


		System.out.println(cutNum.multiply(cutNum).multiply(cutNum));

	}
}
/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