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

public class Main {
	public static void main(String[] args) {

		Scanner sc =new Scanner(System.in);
		double l=sc.nextDouble();
		BigDecimal side1 = new BigDecimal(l/3);
		BigDecimal side2 = new BigDecimal(l/3);
		BigDecimal side3 = new BigDecimal(l/3);
		System.out.println(side1.multiply(side2).multiply(side3));
	}
}
/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