Problem:
Score : 500 points

Problem Statement

N players will participate in a tennis tournament. We will call them Player 1, Player 2, \ldots, Player N.

The tournament is round-robin format, and there will be N(N-1)/2 matches in total.
Is it possible to schedule these matches so that all of the following conditions are satisfied? If the answer is yes, also find the minimum number of days required.

Each player plays at most one matches in a day.

Each player i (1 \leq i \leq N) plays one match against Player A_{i, 1}, A_{i, 2}, \ldots, A_{i, N-1} in this order.

Constraints

3 \leq N \leq 1000

1 \leq A_{i, j} \leq N

A_{i, j} \neq i

A_{i, 1}, A_{i, 2}, \ldots, A_{i, N-1} are all different.

Input

Input is given from Standard Input in the following format:

N
A_{1, 1} A_{1, 2} \ldots A_{1, N-1}
A_{2, 1} A_{2, 2} \ldots A_{2, N-1}
:
A_{N, 1} A_{N, 2} \ldots A_{N, N-1}

Output

If it is possible to schedule all the matches so that all of the conditions are satisfied, print the minimum number of days required; if it is impossible, print -1.

Sample Input 1

3
2 3
1 3
1 2

Sample Output 1

3

All the conditions can be satisfied if the matches are scheduled for three days as follows:

Day 1: Player 1 vs Player 2

Day 2: Player 1 vs Player 3

Day 3: Player 2 vs Player 3

This is the minimum number of days required.

Sample Input 2

4
2 3 4
1 3 4
4 1 2
3 1 2

Sample Output 2

4

All the conditions can be satisfied if the matches are scheduled for four days as follows:

Day 1: Player 1 vs Player 2, Player 3 vs Player 4

Day 2: Player 1 vs Player 3

Day 3: Player 1 vs Player 4, Player 2 vs Player 3

Day 4: Player 2 vs Player 4

This is the minimum number of days required.

Sample Input 3

3
2 3
3 1
1 2

Sample Output 3

-1

Any scheduling of the matches violates some condition.

Solution in Common Lisp (SBCL 1.1.14) (judge verdict: Accepted)

#-swank
(unless (member :child-sbcl *features*)
  (quit
   :unix-status
   (process-exit-code
    (run-program *runtime-pathname*
                 `("--control-stack-size" "256MB"
                   "--noinform" "--disable-ldb" "--lose-on-corruption" "--end-runtime-options"
                   "--eval" "(push :child-sbcl *features*)"
                   "--script" ,(namestring *load-pathname*))
                 :output t :error t :input t))))
;; -*- coding: utf-8 -*-
(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)) (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*))
  (declare #.OPT)
  (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))))))))

;;;
;;; Topological sort
;;;

(define-condition cycle-detected-error (simple-error)
  ((graph :initarg :graph :reader cycle-detected-error-graph)
   (vertex :initarg :vertex :reader cycle-detected-error-vertex))
  (:report
   (lambda (condition stream)
     (format stream "Detected a cycle containing ~A in ~A."
             (cycle-detected-error-vertex condition)
             (cycle-detected-error-graph condition)))))

(declaim (ftype (function * (values (simple-array (integer 0 #.most-positive-fixnum) (*)) &optional))
                topological-sort))
(defun topological-sort (graph)
  "Returns a topologically sorted array of all the vertex in GRAPH. This
function signals CYCLE-DETECTED-ERROR when it detects a cycle.

GRAPH := vector of adjacency lists."
  (declare #.OPT
           ((simple-array list (*)) graph))
  (let* ((n (length graph))
         (tmp-marked (make-array n :element-type 'bit :initial-element 0))
         (marked (make-array n :element-type 'bit :initial-element 0))
         (result (make-array n :element-type '(integer 0 #.most-positive-fixnum)))
         (index (- n 1)))
    (declare (fixnum index))
    (labels ((visit (v)
               (when (= 0 (aref marked v))
                 (when (= 1 (aref tmp-marked v))
                   (error 'cycle-detected-error :graph graph :vertex v))
                 (setf (aref tmp-marked v) 1)
                 (dolist (next (aref graph v))
                   (visit next))
                 (setf (aref marked v) 1)
                 (setf (aref result index) v)
                 (decf index))))
      (dotimes (v n result)
        (when (= 0 (aref marked v))
          (visit v))))))

(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
;;;

(declaim (inline encode))
(defun encode (x y)
  (when (> x y)
    (rotatef x y))
  (dpb y (byte 10 10) x))

(defconstant +max+ (ash 1 20))

(defun main ()
  (declare #.OPT)
  (let* ((n (read))
         (as (make-array (list n (- n 1)) :element-type 'uint32))
         (graph (make-array +max+ :element-type 'list :initial-element nil)))
    (declare (uint16 n))
    (dotimes (i n)
      (dotimes (j (- n 1))
        (let ((a (- (read-fixnum) 1)))
          (setf (aref as i j) a))))
    (dotimes (i n)
      (dotimes (j (- n 2))
        (let* ((op1 (aref as i j))
               (op2 (aref as i (+ j 1)))
               (v1 (encode i op1))
               (v2 (encode i op2)))
          (push v2 (aref graph v1)))))
    (handler-bind ((cycle-detected-error
                     (lambda (c) (println -1) (return-from main))))
      (let ((seq (topological-sort graph))
            (dp (make-array +max+ :element-type 'uint32 :initial-element 1)))
        (dotimes (i +max+)
          (let ((v (aref seq i)))
            (dolist (neighbor (aref graph v))
              (setf (aref dp neighbor)
                    (max (aref dp neighbor)
                         (+ 1 (aref dp v)))))))
        (println (reduce #'max dp))))))

#-swank (main)