import java.util.*;
import java.math.BigDecimal;
 
public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double L = sc.nextDouble();
		//double taiseki = Math.pow(L/3.0,3.0);
		//System.out.println(taiseki);
		BigDecimal ans = new BigDecimal(Math.pow((L/3),3));
		System.out.println(ans.toPlainString());
	}
}
/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