import java.util.*;
import java.math.RoundingMode;
import java.math.BigDecimal;
 
public class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		double L = sc.nextInt();
		BigDecimal ans = BigDecimal.valueOf(L*L*L);
		BigDecimal div = BigDecimal.valueOf(27);
		ans = ans.divide(div,7,RoundingMode.HALF_UP);
		System.out.println(ans);
	}
}
/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