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

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int L = sc.nextInt();
		
		BigDecimal bd1 = BigDecimal.valueOf(L*L*L);
		BigDecimal bd2 = new BigDecimal(27);
		
		BigDecimal bd3 = bd1.divide(bd2,10, RoundingMode.HALF_UP);

		
		System.out.println(bd3);
	}
}
/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