import java.math.BigDecimal;
import java.util.*;
import static java.lang.System.out;

public class Main {
    public static void main(String... args) {
        Scanner sc = new Scanner(System.in);
        int l = sc.nextInt();
        BigDecimal decimalL = new BigDecimal(l);
        BigDecimal height = decimalL.divide(new BigDecimal(3),7, BigDecimal.ROUND_HALF_DOWN);
        BigDecimal ans = height.multiply(height).multiply(height);
        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