(defconstant +inf+ 987654321987654321)

(defun main (&rest argv)
  (declare (ignorable argv))
  (let* ((*read-default-float-format* 'double-float)
         (n (read))
         (p (read))
         (h (make-array n :element-type 'integer))
         (dp1 (make-array n :element-type 'integer :initial-element +inf+))
         (dp2 (make-array n :element-type 'integer :initial-element +inf+)))
    (dotimes (i n) (setf (aref h i) (read)))
    (setf (aref dp1 0) 0)
    (loop for i from 1 below n do
          (setf (aref dp1 i) (min (+ p (aref dp2 (1- i))) (+ (aref dp1 (1- i)) (min (max (- (aref h i) (aref h (1- i))) 0) p)))
                (aref dp2 i) (min (+ p (aref dp1 (1- i))) (+ (aref dp2 (1- i)) (min (max (- (aref h (1- i)) (aref h i)) 0) p)))))
    (format t "~d~%" (min (aref dp1 (1- n)) (aref dp2 (1- n))))))

(main)