Problem:
Score : 600 points

Problem Statement

We have N points numbered 1 to N arranged in a line in this order.

Takahashi decides to make an undirected graph, using these points as the vertices.
In the beginning, the graph has no edge. Takahashi will do M operations to add edges in this graph.
The i-th operation is as follows:

The operation uses integers L_i and R_i between 1 and N (inclusive), and a positive integer C_i. For every pair of integers (s, t) such that L_i \leq s < t \leq R_i, add an edge of length C_i between Vertex s and Vertex t.

The integers L_1, ..., L_M, R_1, ..., R_M, C_1, ..., C_M are all given as input.

Takahashi wants to solve the shortest path problem in the final graph obtained. Find the length of the shortest path from Vertex 1 to Vertex N in the final graph.

Constraints

2 \leq N \leq 10^5

1 \leq M \leq 10^5

1 \leq L_i < R_i \leq N

1 \leq C_i \leq 10^9

Input

Input is given from Standard Input in the following format:

N M
L_1 R_1 C_1
:
L_M R_M C_M

Output

Print the length of the shortest path from Vertex 1 to Vertex N in the final graph.
If there is no shortest path, print -1 instead.

Sample Input 1

4 3
1 3 2
2 4 3
1 4 6

Sample Output 1

5

We have an edge of length 2 between Vertex 1 and Vertex 2, and an edge of length 3 between Vertex 2 and Vertex 4, so there is a path of length 5 between Vertex 1 and Vertex 4.

Sample Input 2

4 2
1 2 1
3 4 2

Sample Output 2

-1

Sample Input 3

10 7
1 5 18
3 4 8
1 3 5
4 7 10
5 9 8
6 10 5
8 10 3

Sample Output 3

28

Solution in Common Lisp (SBCL 2.0.3) (judge verdict: Accepted)

(in-package :cl-user)
(eval-when (:compile-toplevel :load-toplevel :execute)
  (sb-int:defconstant-eqx opt
    #+swank '(optimize (speed 3) (safety 2))
    #-swank '(optimize (speed 3) (safety 0) (debug 0))
    #'equal)
  #+swank (ql:quickload '(:cl-debug-print :fiveam) :silent t)
  #-swank (set-dispatch-macro-character
           #\# #\> (lambda (s c p) (declare (ignore c p)) `(values ,(read s nil nil t)))))
#+swank (set-dispatch-macro-character #\# #\> #'cl-debug-print:debug-print-reader)

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

(defconstant +mod+ 1000000007)

(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)))

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

;; BEGIN_INSERTED_CONTENTS
;;;
;;; Implicit treap
;;; (treap with implicit key)
;;;

;; TODO: abstraction

(defpackage :cp/implicit-treap
  (:use :cl)
  (:export #:itreap #:itreap-p #:itreap-count #:itreap-accumulator
           #:make-itreap #:invalid-itreap-index-error #:itreap-ref
           #:itreap-split #:itreap-merge #:itreap-insert #:itreap-delete
           #:itreap-push #:itreap-pop #:itreap-map #:do-itreap
           #:itreap-fold #:itreap-fold-bisect #:itreap-fold-bisect-from-end
           #:itreap-update #:itreap-reverse
           #:itreap-bisect-left #:itreap-bisect-right #:itreap-insort))
(in-package :cp/implicit-treap)

;; Note:
;; - An empty treap is NIL.

(declaim (inline op))
(defun op (a b)
  "Is a binary operator comprising a monoid."
  (min a b))

(defconstant +op-identity+ most-positive-fixnum
  "identity element w.r.t. OP")

(declaim (inline updater-op))
(defun updater-op (lazy x)
  "Is the operator to compute and update LAZY value. LAZY is the current LAZY
value and X is an operand."
  (min lazy x))

(defconstant +updater-identity+ most-positive-fixnum
  "identity element w.r.t. UPDATER-OP")

(declaim (inline modifier-op))
(defun modifier-op (acc lazy size)
  "Is the operator to update ACCUMULATOR (and VALUE) based on LAZY value. ACC is
the current ACCUMULATOR value and LAZY is the LAZY value. SIZE is the length of
the target interval."
  (declare (ignorable size))
  (min acc lazy))

(defstruct (itreap (:constructor %make-itreap (value priority &key left right (count 1) (accumulator value) (lazy +updater-identity+)))
                   (:copier nil)
                   (:conc-name %itreap-))
  (value +op-identity+ :type fixnum)
  (accumulator +op-identity+ :type fixnum)
  (lazy +updater-identity+ :type fixnum)
  (priority 0 :type (integer 0 #.most-positive-fixnum))
  (count 1 :type (mod #.most-positive-fixnum)) ; size of (sub)treap
  (left nil :type (or null itreap))
  (right nil :type (or null itreap)))

(declaim (inline itreap-count))
(defun itreap-count (itreap)
  "Returns the number of the elements of ITREAP."
  (declare ((or null itreap) itreap))
  (if itreap
      (%itreap-count itreap)
      0))

(declaim (inline itreap-accumulator))
(defun itreap-accumulator (itreap)
  "Returns the sum (w.r.t. OP) of the whole ITREAP:
ITREAP[0]+ITREAP[1]+...+ITREAP[SIZE-1]."
  (declare ((or null itreap) itreap))
  (if itreap
      (%itreap-accumulator itreap)
      +op-identity+))

(declaim (inline update-count))
(defun update-count (itreap)
  (declare (itreap itreap))
  (setf (%itreap-count itreap)
        (+ 1
           (itreap-count (%itreap-left itreap))
           (itreap-count (%itreap-right itreap)))))

(declaim (inline update-accumulator))
(defun update-accumulator (itreap)
  (declare (itreap itreap))
  (setf (%itreap-accumulator itreap)
        (if (%itreap-left itreap)
            (if (%itreap-right itreap)
                (let ((mid (op (%itreap-accumulator (%itreap-left itreap))
                               (%itreap-value itreap))))
                  (op mid (%itreap-accumulator (%itreap-right itreap))))
                (op (%itreap-accumulator (%itreap-left itreap))
                    (%itreap-value itreap)))
            (if (%itreap-right itreap)
                (op (%itreap-value itreap)
                    (%itreap-accumulator (%itreap-right itreap)))
                (%itreap-value itreap)))))

(declaim (inline force-up))
(defun force-up (itreap)
  "Propagates up the information from children."
  (declare (itreap itreap))
  (update-count itreap)
  (update-accumulator itreap))

(declaim (inline force-down))
(defun force-down (itreap)
  "Propagates down the information to children."
  (declare (itreap itreap))
  (unless (eql +updater-identity+ (%itreap-lazy itreap))
    (when (%itreap-left itreap)
      (setf (%itreap-lazy (%itreap-left itreap))
            (updater-op (%itreap-lazy (%itreap-left itreap))
                        (%itreap-lazy itreap)))
      (setf (%itreap-accumulator (%itreap-left itreap))
            (modifier-op (%itreap-accumulator (%itreap-left itreap))
                         (%itreap-lazy itreap)
                         (%itreap-count (%itreap-left itreap)))))
    (when (%itreap-right itreap)
      (setf (%itreap-lazy (%itreap-right itreap))
            (updater-op (%itreap-lazy (%itreap-right itreap))
                        (%itreap-lazy itreap)))
      (setf (%itreap-accumulator (%itreap-right itreap))
            (modifier-op (%itreap-accumulator (%itreap-right itreap))
                         (%itreap-lazy itreap)
                         (%itreap-count (%itreap-right itreap)))))
    (setf (%itreap-value itreap)
          (modifier-op (%itreap-value itreap)
                       (%itreap-lazy itreap)
                       1))
    (setf (%itreap-lazy itreap) +updater-identity+)))

(defun %heapify (node)
  "Makes it max-heap w.r.t. priorities by swapping the priorities of the whole
treap."
  (declare (optimize (speed 3) (safety 0)))
  (when node
    (let ((high-priority-node node))
      (when (and (%itreap-left node)
                 (> (%itreap-priority (%itreap-left node))
                    (%itreap-priority high-priority-node)))
        (setq high-priority-node (%itreap-left node)))
      (when (and (%itreap-right node)
                 (> (%itreap-priority (%itreap-right node))
                    (%itreap-priority high-priority-node)))
        (setq high-priority-node (%itreap-right node)))
      (unless (eql high-priority-node node)
        (rotatef (%itreap-priority high-priority-node)
                 (%itreap-priority node))
        (%heapify high-priority-node)))))

(declaim (inline make-itreap))
(defun make-itreap (size &key initial-contents)
  "Makes a treap of SIZE in O(SIZE) time. Its values are filled with the
identity element unless INITIAL-CONTENTS are supplied."
  (declare ((or null vector) initial-contents))
  (labels ((build (l r)
             (declare ((integer 0 #.most-positive-fixnum) l r))
             (if (= l r)
                 nil
                 (let* ((mid (ash (+ l r) -1))
                        (node (%make-itreap (if initial-contents
                                                (aref initial-contents mid)
                                                +op-identity+)
                                            (random most-positive-fixnum))))
                   (setf (%itreap-left node) (build l mid))
                   (setf (%itreap-right node) (build (+ mid 1) r))
                   (%heapify node)
                   (force-up node)
                   node))))
    (build 0 size)))

(define-condition invalid-itreap-index-error (type-error)
  ((itreap :initarg :itreap :reader invalid-itreap-index-error-itreap)
   (index :initarg :index :reader invalid-itreap-index-error-index))
  (:report
   (lambda (condition stream)
     (let ((index (invalid-itreap-index-error-index condition)))
       (if (consp index)
           (format stream "Invalid range [~W, ~W) for itreap ~W."
                   (car index)
                   (cdr index)
                   (invalid-itreap-index-error-itreap condition))
           (format stream "Invalid index ~W for itreap ~W."
                   index
                   (invalid-itreap-index-error-itreap condition)))))))

(defun itreap-split (itreap index)
  "Destructively splits ITREAP at INDEX and returns two treaps (in ascending
order)."
  (declare (optimize (speed 3))
           ((integer 0 #.most-positive-fixnum) index))
  (unless (<= index (itreap-count itreap))
    (error 'invalid-itreap-index-error :index index :itreap itreap))
  (labels ((recur (itreap ikey)
             (unless itreap
               (return-from itreap-split (values nil nil)))
             (force-down itreap)
             (let ((left-count (itreap-count (%itreap-left itreap))))
               (if (<= ikey left-count)
                   (multiple-value-bind (left right)
                       (itreap-split (%itreap-left itreap) ikey)
                     (setf (%itreap-left itreap) right)
                     (force-up itreap)
                     (values left itreap))
                   (multiple-value-bind (left right)
                       (itreap-split (%itreap-right itreap) (- ikey left-count 1))
                     (setf (%itreap-right itreap) left)
                     (force-up itreap)
                     (values itreap right))))))
    (recur itreap index)))

(defun itreap-merge (left right)
  "Destructively concatenates two ITREAPs. Note that this `merge' is different
from CL:MERGE and rather close to CL:CONCATENATE."
  (declare (optimize (speed 3))
           ((or null itreap) left right))
  (cond ((null left) (when right (force-down right) (force-up right)) right)
        ((null right) (when left (force-down left) (force-up left)) left)
        (t (force-down left)
           (force-down right)
           (if (> (%itreap-priority left) (%itreap-priority right))
               (progn
                 (setf (%itreap-right left)
                       (itreap-merge (%itreap-right left) right))
                 (force-up left)
                 left)
               (progn
                 (setf (%itreap-left right)
                       (itreap-merge left (%itreap-left right)))
                 (force-up right)
                 right)))))

(defun itreap-insert (itreap index obj)
  "Destructively inserts OBJ into ITREAP at INDEX and returns the resultant treap.

You cannot rely on the side effect. Use the returned value."
  (declare (optimize (speed 3))
           ((or null itreap) itreap)
           ((integer 0 #.most-positive-fixnum) index))
  (unless (<= index (itreap-count itreap))
    (error 'invalid-itreap-index-error :itreap itreap :index index))
  (let ((node (%make-itreap obj (random most-positive-fixnum))))
    (labels ((recur (itreap ikey)
               (declare ((integer 0 #.most-positive-fixnum) ikey))
               (unless itreap (return-from recur node))
               (force-down itreap)
               (if (> (%itreap-priority node) (%itreap-priority itreap))
                   (progn
                     (setf (values (%itreap-left node) (%itreap-right node))
                           (itreap-split itreap ikey))
                     (force-up node)
                     node)
                   (let ((left-count (itreap-count (%itreap-left itreap))))
                     (if (<= ikey left-count)
                         (setf (%itreap-left itreap)
                               (recur (%itreap-left itreap) ikey))
                         (setf (%itreap-right itreap)
                               (recur (%itreap-right itreap) (- ikey left-count 1))))
                     (force-up itreap)
                     itreap))))
      (recur itreap index))))

(defun itreap-delete (itreap index)
  "Destructively deletes the object at INDEX in ITREAP.

You cannot rely on the side effect. Use the returned value."
  (declare (optimize (speed 3))
           ((integer 0 #.most-positive-fixnum) index))
  (unless (< index (itreap-count itreap))
    (error 'invalid-itreap-index-error :itreap itreap :index index))
  (labels ((recur (itreap ikey)
             (declare ((integer 0 #.most-positive-fixnum) ikey))
             (force-down itreap)
             (let ((left-count (itreap-count (%itreap-left itreap))))
               (cond ((< ikey left-count)
                      (setf (%itreap-left itreap)
                            (recur (%itreap-left itreap) ikey))
                      (force-up itreap)
                      itreap)
                     ((> ikey left-count)
                      (setf (%itreap-right itreap)
                            (recur (%itreap-right itreap) (- ikey left-count 1)))
                      (force-up itreap)
                      itreap)
                     (t
                      (itreap-merge (%itreap-left itreap) (%itreap-right itreap)))))))
    (recur itreap index)))

(defmacro itreap-push (obj itreap pos)
  "Pushes OBJ to ITREAP at POS."
  `(setf ,itreap (itreap-insert ,itreap ,pos ,obj)))

(defmacro itreap-pop (itreap pos)
  "Returns the object at POS and deletes it."
  (let ((p (gensym)))
    `(let ((,p ,pos))
       (prog1 (itreap-ref ,itreap ,p)
         (setf ,itreap (itreap-delete ,itreap ,p))))))

(declaim (inline itreap-map))
(defun itreap-map (function itreap)
  "Successively applies FUNCTION to ITREAP[0], ..., ITREAP[SIZE-1]."
  (declare (function function))
  (labels ((recur (node)
             (when node
               (force-down node)
               (recur (%itreap-left node))
               (funcall function (%itreap-value node))
               (recur (%itreap-right node))
               (force-up node))))
    (recur itreap)))

(defmethod print-object ((object itreap) stream)
  (print-unreadable-object (object stream :type t)
    (let ((init t))
      (itreap-map (lambda (x)
                    (if init
                        (setq init nil)
                        (write-char #\  stream))
                    (write x :stream stream))
                  object))))

(defmacro do-itreap ((var itreap &optional result) &body body)
  "Successively binds ITREAP[0], ..., ITREAP[SIZE-1] to VAR and executes BODY
each time."
  `(block nil
     (itreap-map (lambda (,var) ,@body) ,itreap)
     ,result))

(defun itreap (&rest args)
  ;; NOTE: This function takes O(nlog(n)) time. Use MAKE-ITREAP for efficiency.
  (labels ((recur (list position itreap)
             (declare ((integer 0 #.most-positive-fixnum) position))
             (if (null list)
                 itreap
                 (recur (cdr list)
                        (1+ position)
                        (itreap-insert itreap position (car list))))))
    (recur args 0 nil)))

(declaim (inline itreap-ref))
(defun itreap-ref (itreap index)
  "Returns the element ITREAP[INDEX]."
  (declare ((integer 0 #.most-positive-fixnum) index))
  (unless (< index (itreap-count itreap))
    (error 'invalid-itreap-index-error :itreap itreap :index index))
  (labels ((%ref (itreap index)
             (declare ((integer 0 #.most-positive-fixnum) index))
             (force-down itreap)
             (prog1
                 (let ((left-count (itreap-count (%itreap-left itreap))))
                   (cond ((< index left-count)
                          (%ref (%itreap-left itreap) index))
                         ((> index left-count)
                          (%ref (%itreap-right itreap) (- index left-count 1)))
                         (t (%itreap-value itreap))))
               (force-up itreap))))
    (%ref itreap index)))

(declaim (inline (setf itreap-ref)))
(defun (setf itreap-ref) (new-value itreap index)
  "Sets ITREAP[INDEX] to the given value."
  (declare ((integer 0 #.most-positive-fixnum) index))
  (unless (< index (itreap-count itreap))
    (error 'invalid-itreap-index-error :itreap itreap :index index))
  (labels ((%set (itreap index)
             (declare ((integer 0 #.most-positive-fixnum) index))
             (force-down itreap)
             (prog1
                 (let ((left-count (itreap-count (%itreap-left itreap))))
                   (cond ((< index left-count)
                          (%set (%itreap-left itreap) index))
                         ((> index left-count)
                          (%set (%itreap-right itreap) (- index left-count 1)))
                         (t (setf (%itreap-value itreap) new-value))))
               (force-up itreap))))
    (%set itreap index)
    new-value))

(declaim (inline itreap-fold))
(defun itreap-fold (itreap l r)
  "Returns the `sum' (w.r.t. OP) of the range ITREAP[L, R)."
  (declare ((integer 0 #.most-positive-fixnum) l r))
  (unless (<= l r (itreap-count itreap))
    (error 'invalid-itreap-index-error :itreap itreap :index (cons l r)))
  (labels
      ((recur (itreap l r)
         (declare ((integer 0 #.most-positive-fixnum) l r))
         (unless itreap
           (return-from recur +op-identity+))
         (force-down itreap)
         (prog1
             (if (and (zerop l) (= r (%itreap-count itreap)))
                 (itreap-accumulator itreap)
                 (let ((left-count (itreap-count (%itreap-left itreap))))
                   (if (<= l left-count)
                       (if (< left-count r)
                           ;; LEFT-COUNT is in [L, R)
                           (op (op (recur (%itreap-left itreap) l (min r left-count))
                                   (%itreap-value itreap))
                               (recur (%itreap-right itreap) 0 (- r left-count 1)))
                           ;; LEFT-COUNT is in [R, END)
                           (recur (%itreap-left itreap) l (min r left-count)))
                       ;; LEFT-COUNT is in [0, L)
                       (recur (%itreap-right itreap) (- l left-count 1) (- r left-count 1)))))
           (force-up itreap))))
    (recur itreap l r)))

;; FIXME: might be problematic when two priorities collide and START is not
;; zero. (It will be negligible from the viewpoint of probability, however.)
(declaim (inline itreap-fold-bisect))
(defun itreap-fold-bisect (itreap test &optional (start 0))
  "Returns the largest index that satisfies (FUNCALL TEST (OP ITREAP[START]
ITREAP[START+1] ... ITREAP[index-1])).

Note:
- (FUNCALL TEST +OP-IDENTITY+) must be true.
- TEST must be monotone in the target range.
"
  (declare ((integer 0 #.most-positive-fixnum) start))
  (assert (funcall test +op-identity+))
  (multiple-value-bind (itreap-prefix itreap)
      (if (zerop start)
          (values nil itreap)
          (itreap-split itreap start))
    (labels
        ((recur (itreap offset prev-sum)
           (declare ((integer 0 #.most-positive-fixnum) offset)
                    #+sbcl (values (integer 0 #.most-positive-fixnum)))
           (unless itreap
             (return-from recur offset))
           (force-down itreap)
           (let ((sum prev-sum))
             (prog1
                 (cond ((not (funcall test (setq sum (op sum (itreap-accumulator (%itreap-left itreap))))))
                        (recur (%itreap-left itreap) offset prev-sum))
                       ((not (funcall test (setq sum (op sum (%itreap-value itreap)))))
                        (+ offset (itreap-count (%itreap-left itreap))))
                       (t
                        (recur (%itreap-right itreap)
                               (+ offset (itreap-count (%itreap-left itreap)) 1)
                               sum)))
               (force-up itreap)))))
      (prog1 (+ start (recur itreap 0 +op-identity+))
        (itreap-merge itreap-prefix itreap)))))

(declaim (inline itreap-fold-bisect-from-end))
(defun itreap-fold-bisect-from-end (itreap test &optional end)
  "Returns the smallest index that satisfies (FUNCALL TEST (OP ITREAP[index]
  ITREAP[index+1] ... ITREAP[END-1])).

Note:
- (FUNCALL TEST +OP-IDENTITY+) must be true.
- TEST must be monotone in the target range.
"
  (declare ((or null (integer 0 #.most-positive-fixnum)) end))
  (assert (funcall test +op-identity+))
  (multiple-value-bind (itreap itreap-suffix)
      (if end
          (itreap-split itreap end)
          (values itreap nil))
    (labels
        ((recur (itreap offset prev-sum)
           (declare ((integer 0 #.most-positive-fixnum) offset)
                    #+sbcl (values (integer 0 #.most-positive-fixnum)))
           (unless itreap
             (return-from recur offset))
           (force-down itreap)
           (let ((sum prev-sum))
             (prog1
                 (cond ((not (funcall test (setq sum (op (itreap-accumulator (%itreap-right itreap)) sum))))
                        (recur (%itreap-right itreap) offset prev-sum))
                       ((not (funcall test (setq sum (op (%itreap-value itreap) sum))))
                        (+ offset (itreap-count (%itreap-right itreap))))
                       (t
                        (recur (%itreap-left itreap)
                               (+ offset (itreap-count (%itreap-right itreap)) 1)
                               sum)))
               (force-up itreap)))))
      (prog1 (- (or end (itreap-count itreap))
                (recur itreap 0 +op-identity+))
        (itreap-merge itreap itreap-suffix)))))

(declaim (inline itreap-update))
(defun itreap-update (itreap operand l r)
  "Updates ITRAP by ITREAP[i] := (OP ITREAP[i] OPERAND) for all i in [l, r)"
  (declare ((integer 0 #.most-positive-fixnum) l r))
  (unless (<= l r (itreap-count itreap))
    (error 'invalid-itreap-index-error :itreap itreap :index (cons l r)))
  (labels
      ((recur (itreap l r)
         (declare ((integer 0 #.most-positive-fixnum) l r))
         (when itreap
           (if (and (zerop l) (= r (%itreap-count itreap)))
               (progn
                 (setf (%itreap-lazy itreap)
                       (updater-op (%itreap-lazy itreap) operand))
                 (force-down itreap))
               (let ((left-count (itreap-count (%itreap-left itreap))))
                 (force-down itreap)
                 (if (<= l left-count)
                     (if (< left-count r)
                         ;; LEFT-COUNT is in [L, R)
                         (progn
                           (recur (%itreap-left itreap) l (min r left-count))
                           (setf (%itreap-value itreap)
                                 (modifier-op (%itreap-value itreap) operand 1))
                           (recur (%itreap-right itreap) 0 (- r left-count 1)))
                         ;; LEFT-COUNT is in [R, END)
                         (recur (%itreap-left itreap) l (min r left-count)))
                     ;; LEFT-COUNT is in [0, L)
                     (recur (%itreap-right itreap) (- l left-count 1) (- r left-count 1)))))
           (force-up itreap))))
    (recur itreap l r)
    itreap))

;;;
;;; Below are utilities for treap whose values are sorted w.r.t. some order
;;;

(declaim (inline itreap-bisect-left)
         (ftype (function * (values (integer 0 #.most-positive-fixnum) &optional)) itreap-bisect-left))
(defun itreap-bisect-left (itreap value order)
  "Takes a **sorted** treap and returns the smallest index that satisfies
ITREAP[index] >= VALUE, where >= is the complement of ORDER. In other words,
this function returns a leftmost index at which value can be inserted with
keeping the order. Returns the size of ITREAP if ITREAP[length-1] <
VALUE. The time complexity is O(log(n))."
  (labels ((recur (count itreap)
             (declare ((integer 0 #.most-positive-fixnum) count))
             (cond ((null itreap) nil)
                   ((funcall order (%itreap-value itreap) value)
                    (recur count (%itreap-right itreap)))
                   (t
                    (let ((left-count (- count (itreap-count (%itreap-right itreap)) 1)))
                      (or (recur left-count (%itreap-left itreap))
                          left-count))))))
    (or (recur (itreap-count itreap) itreap)
        (itreap-count itreap))))

(declaim (inline itreap-bisect-right)
         (ftype (function * (values (integer 0 #.most-positive-fixnum) &optional)) itreap-bisect-right))
(defun itreap-bisect-right (itreap value order)
  "Takes a **sorted** treap and returns the smallest index that satisfies
VALUE < ITREAP[index], where < is ORDER. In other words, this function
returns a rightmost index at which VALUE can be inserted with keeping the
order. Returns the size of ITREAP if ITREAP[length-1] <= VALUE. The time
complexity is O(log(n))."
  (labels ((recur (count itreap)
             (declare ((integer 0 #.most-positive-fixnum) count))
             (cond ((null itreap) nil)
                   ((funcall order value (%itreap-value itreap))
                    (let ((left-count (- count (itreap-count (%itreap-right itreap)) 1)))
                      (or (recur left-count (%itreap-left itreap))
                          left-count)))
                   (t
                    (recur count (%itreap-right itreap))))))
    (or (recur (itreap-count itreap) itreap)
        (itreap-count itreap))))

(declaim (inline itreap-insort))
(defun itreap-insort (itreap obj order)
  "Does insertion to the sorted treap with keeping the order. You cannot rely on
the side effect. Use the returned value."
  (let ((pos (itreap-bisect-left itreap obj order)))
    (itreap-insert itreap pos obj)))

(defpackage :cp/read-fixnum
  (:use :cl)
  (:export #:read-fixnum))
(in-package :cp/read-fixnum)

(declaim (ftype (function * (values fixnum &optional)) read-fixnum))
(defun read-fixnum (&optional (in *standard-input*))
  "NOTE: cannot read -2^62"
  (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 #\-))
                                  (setq 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))))))))

;; BEGIN_USE_PACKAGE
(eval-when (:compile-toplevel :load-toplevel :execute)
  (use-package :cp/read-fixnum :cl-user))
(eval-when (:compile-toplevel :load-toplevel :execute)
  (use-package :cp/implicit-treap :cl-user))
(in-package :cl-user)

;;;
;;; Body
;;;

(defun main ()
  (let* ((n (read))
         (m (read))
         (events (make-array n :element-type 'list :initial-element nil))
         (itreap (make-itreap n)))
    (dotimes (i m)
      (let ((l (- (read-fixnum) 1))
            (r (read-fixnum))
            (c (read-fixnum)))
        (push (cons r c) (aref events l))))
    (setf (itreap-ref itreap 0) 0)
    (dotimes (l n)
      #>itreap
      (let ((dist (itreap-ref itreap l)))
        (unless (= dist most-positive-fixnum)
          (loop for (r . c) in (aref events l)
                do (dbg l r c) (itreap-update itreap (+ dist c) l r)))))
    (let ((res (itreap-ref itreap (- n 1))))
      (println (if (= res most-positive-fixnum)
                   -1
                   res)))))

#-swank (main)

;;;
;;; Test and benchmark
;;;

#+swank
(defun get-clipbrd ()
  (with-output-to-string (out)
    #+os-windows (run-program "powershell.exe" '("-Command" "Get-Clipboard") :output out :search t)
    #+os-unix (run-program "xsel" '("-b" "-o") :output out :search t)))

#+swank (defparameter *this-pathname* (uiop:current-lisp-file-pathname))
#+swank (defparameter *dat-pathname* (uiop:merge-pathnames* "test.dat" *this-pathname*))

#+swank
(defun run (&optional thing (out *standard-output*))
  "THING := null | string | symbol | pathname

null: run #'MAIN using the text on clipboard as input.
string: run #'MAIN using the string as input.
symbol: alias of FIVEAM:RUN!.
pathname: run #'MAIN using the text file as input."
  (let* ((*standard-output* (or out (make-string-output-stream)))
         (res (etypecase thing
                (null
                 (with-input-from-string (*standard-input* (delete #\Return (get-clipbrd)))
                   (main)))
                (string
                 (with-input-from-string (*standard-input* (delete #\Return thing))
                   (main)))
                (symbol (5am:run! thing))
                (pathname
                 (with-open-file (*standard-input* thing)
                   (main))))))
    (if out res (get-output-stream-string *standard-output*))))

#+swank
(defun gen-dat ()
  (uiop:with-output-file (out *dat-pathname* :if-exists :supersede)
    (format out "")))

#+swank
(defun bench (&optional (out (make-broadcast-stream)))
  (time (run *dat-pathname* out)))

#-swank
(eval-when (:compile-toplevel)
  (when (and (boundp 'sb-c::*compiler-warning-count*)
             (> sb-c::*compiler-warning-count* 0))
    (sb-ext:quit :unix-status 1)))

;; To run: (5am:run! :sample)
#+swank
(it.bese.fiveam:test :sample
  (5am:is
   (equal "5
"
          (run "4 3
1 3 2
2 4 3
1 4 6
" nil)))
  (5am:is
   (equal "-1
"
          (run "4 2
1 2 1
3 4 2
" nil)))
  (5am:is
   (equal "28
"
          (run "10 7
1 5 18
3 4 8
1 3 5
4 7 10
5 9 8
6 10 5
8 10 3
" nil))))