(defconstant +inf+ 987654321987654321)

(defun main (&rest argv)
  (declare (ignorable argv))
  (let* ((*read-default-float-format* 'double-float)
         (n (read))
         (p (read))
         (dp1 (make-array 15015 :element-type 'integer :initial-element +inf+)))
    (setf (aref dp1 0) 0)
    (dotimes (_ n)
      (let* ((a (read))
             (b (read))
             (c (read))
             (dp2 (make-array 15015 :element-type 'integer :initial-element +inf+)))
        (loop for j to (* 3 n) do
              (when (>= j 0)
                    (setf (aref dp2 j) (min (aref dp2 j) (+ a (aref dp1 j)))))
              (when (>= j 1)
                    (setf (aref dp2 j) (min (aref dp2 j) (+ b (aref dp1 (- j 1))))))
              (when (>= j 2)
                    (setf (aref dp2 j) (min (aref dp2 j) (+ c (aref dp1 (- j 2))))))
              (when (>= j 3)
                    (setf (aref dp2 j) (min (aref dp2 j) (+ 1 (aref dp1 (- j 3)))))))
        (replace dp1 dp2)))
    (format t "~f~%" (/ (float (aref dp1 p) 0d0) (float n 0d0)))))

(main)