import java.util.*;
import java.io.*;
import java.math.BigDecimal;
import java.math.RoundingMode;

class Main{
    public static void main(String args[])throws IOException{
        try(BufferedReader br = new BufferedReader(new InputStreamReader(System.in))){
            double input = Double.parseDouble(br.readLine());

            BigDecimal num = new BigDecimal(input);
            BigDecimal three = new BigDecimal(3);
            BigDecimal x = num.divide(three, 6, RoundingMode.HALF_UP);
            BigDecimal answer = x.multiply(x).multiply(x);

            double result = answer.doubleValue();

            System.out.println(result);
        }
   
    }
}
/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