import java.util.*;
import java.math.*;
public class Main {
    public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int totalLength = Integer.parseInt(sc.next());
      	double length=(double)totalLength/3;
    	System.out.println(BigDecimal.valueOf(Math.pow(length,3d)).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