import java.util.*;
import java.math.*;
public class Main {
    public static void main(String[] args){
      // 入力
      Scanner sc = new Scanner(System.in);
      int L = sc.nextInt();
      
      // 体積最大値算出
      BigDecimal bdL = BigDecimal.valueOf(L);
      BigDecimal three = BigDecimal.valueOf(3);
      BigDecimal ave = bdL.divide(three, 6, BigDecimal.ROUND_HALF_UP);
      BigDecimal max = ave;
      max = max.multiply(ave);
      max = max.multiply(ave);
      
      // 出力
      System.out.println(max);
    }
    
}
/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