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

/**
 * @author yoshizaki
 * ABC 159
 */
public class Main {
    public static void main(String[] args) {
        Scanner scanner= new Scanner(System.in);
        BigDecimal l = new BigDecimal(scanner.nextInt());
        BigDecimal edge = l.divide(new BigDecimal(3), 10, BigDecimal.ROUND_HALF_UP); 
        BigDecimal answer = edge.pow(3);
        System.out.println(answer);
    }
}
/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