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

public class Main {

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

		int l = sca.nextInt();

		double i = l/3.0;
		double j = l/3.0;
		double k = l/3.0;
		double max = i*j*k;
		BigDecimal bd = new BigDecimal(max);

		System.out.println(bd.setScale(8, RoundingMode.DOWN));

		// 後始末
		sca.close();
	}
}
/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