;; -*- coding: utf-8 -*-
(eval-when (:compile-toplevel :load-toplevel :execute)
  (defparameter OPT
    #+swank '(optimize (speed 3) (safety 2))
    #-swank '(optimize (speed 3) (safety 0) (debug 0)))
  #+swank (ql:quickload '(:cl-debug-print :fiveam))
  #-swank (set-dispatch-macro-character #\# #\> (lambda (s c p) (declare (ignore c p)) (read s nil (values) t))))
#+swank (cl-syntax:use-syntax cl-debug-print:debug-print-syntax)
#-swank (disable-debugger) ; for CS Academy

;; BEGIN_INSERTED_CONTENTS
(declaim (ftype (function * (values fixnum &optional)) read-fixnum))
(defun read-fixnum (&optional (in *standard-input*))
  (macrolet ((%read-byte ()
               `(the (unsigned-byte 8)
                     #+swank (char-code (read-char in nil #\Nul))
                     #-swank (sb-impl::ansi-stream-read-byte in nil #.(char-code #\Nul) nil))))
    (let* ((minus nil)
           (result (loop (let ((byte (%read-byte)))
                           (cond ((<= 48 byte 57)
                                  (return (- byte 48)))
                                 ((zerop byte) ; #\Nul
                                  (error "Read EOF or #\Nul."))
                                 ((= byte #.(char-code #\-))
                                  (setf minus t)))))))
      (declare ((integer 0 #.most-positive-fixnum) result))
      (loop
        (let* ((byte (%read-byte)))
          (if (<= 48 byte 57)
              (setq result (+ (- byte 48) (* 10 (the (integer 0 #.(floor most-positive-fixnum 10)) result))))
              (return (if minus (- result) result))))))))

(defmacro dbg (&rest forms)
  #+swank
  (if (= (length forms) 1)
      `(format *error-output* "~A => ~A~%" ',(car forms) ,(car forms))
      `(format *error-output* "~A => ~A~%" ',forms `(,,@forms)))
  #-swank (declare (ignore forms)))

(defmacro define-int-types (&rest bits)
  `(progn
     ,@(mapcar (lambda (b) `(deftype ,(intern (format nil "UINT~A" b)) () '(unsigned-byte ,b))) bits)
     ,@(mapcar (lambda (b) `(deftype ,(intern (format nil "INT~A" b)) () '(signed-byte ,b))) bits)))
(define-int-types 2 4 7 8 15 16 31 32 62 63 64)

(declaim (inline println))
(defun println (obj &optional (stream *standard-output*))
  (let ((*read-default-float-format* 'double-float))
    (prog1 (princ obj stream) (terpri stream))))

(defconstant +mod+ 1000000007)

;; Body

(defun main ()
  (let* ((n (read))
         (m (read))
         (p (read))
         (graph (make-array n :element-type 'list :initial-element nil))
         (revgraph (make-array n :element-type 'list :initial-element nil))
         (dp (make-array n :element-type 'fixnum :initial-element most-positive-fixnum)))
    (declare (uint32 n m p))
    (dotimes (i m)
      (let ((a (- (read-fixnum) 1))
            (b (- (read-fixnum) 1))
            (c (read-fixnum)))
        (push (cons b (- p c)) (aref graph a))
        (push a (aref revgraph b))))
    (setf (aref dp 0) 0)
    (dotimes (_ n)
      (dotimes (v n)
        (unless (= (aref dp v) most-positive-fixnum)
          (dolist (node (aref graph v))
            (let ((dest (car node))
                  (cost (cdr node)))
              (declare (fixnum dest cost))
              (setf (aref dp dest)
                    (min (aref dp dest)
                         (+ (aref dp v) cost))))))))
    (let ((cands (make-hash-table)))
      (dotimes (v n)
        (unless (= (aref dp v) most-positive-fixnum)
          (dolist (node (aref graph v))
            (let ((dest (car node))
                  (cost (cdr node)))
              (declare (fixnum dest cost))
              (when (> (aref dp dest) (+ (aref dp v) cost))
                (setf (gethash dest cands) t))))))
      (let ((visited (make-array n :element-type 'bit :initial-element 0)))
        (sb-int:named-let recur ((v (- n 1)))
          (setf (aref visited v) 1)
          (when (gethash v cands)
            (println -1)
            (return-from main cands))
          (dolist (neighbor (aref revgraph v))
            (when (zerop (aref visited neighbor))
              (recur neighbor)))))
      (println (max 0 (- (aref dp (- n 1))))))))

#-swank (main)


Measured memory_bytes: 27236