Problem:
Score : 900 points

Problem Statement

There is a tree with N vertices numbered 1 through N.
The i-th of the N-1 edges connects vertices a_i and b_i.

Initially, each vertex is uncolored.

Takahashi and Aoki is playing a game by painting the vertices. In this game, they alternately perform the following operation, starting from Takahashi:

Select a vertex that is not painted yet.

If it is Takahashi who is performing this operation, paint the vertex white; paint it black if it is Aoki.

Then, after all the vertices are colored, the following procedure takes place:

Repaint every white vertex that is adjacent to a black vertex, in black.

Note that all such white vertices are repainted simultaneously, not one at a time.

If there are still one or more white vertices remaining, Takahashi wins; if all the vertices are now black, Aoki wins.
Determine the winner of the game, assuming that both persons play optimally.

Constraints

2 ≤ N ≤ 10^5

1 ≤ a_i,b_i ≤ N

a_i ≠ b_i

The input graph is a tree.

Input

Input is given from Standard Input in the following format:

N
a_1 b_1
:
a_{N-1} b_{N-1}

Output

Print First if Takahashi wins; print Second if Aoki wins.

Sample Input 1

3
1 2
2 3

Sample Output 1

First

Below is a possible progress of the game:

First, Takahashi paint vertex 2 white.

Then, Aoki paint vertex 1 black.

Lastly, Takahashi paint vertex 3 white.

In this case, the colors of vertices 1, 2 and 3 after the final procedure are black, black and white, resulting in Takahashi's victory.

Sample Input 2

4
1 2
2 3
2 4

Sample Output 2

First

Sample Input 3

6
1 2
2 3
3 4
2 5
5 6

Sample Output 3

Second

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

(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 (cl-syntax:use-syntax cl-debug-print:debug-print-syntax)
#-swank (disable-debugger) ; for CS Academy

;; BEGIN_INSERTED_CONTENTS
;;;
;;; Maximum bipartite matching (Hopcroft-Karp, O(E sqrt(V)))
;;;

;; NOTE: The number of elements in the graph must be less than 2^32-1 as we use
;; (UNSIGNED-BYTE 32) here for efficiency.

;; NOTE: Pay attention to the stack size!

(defconstant +graph-inf-distance+ #xffffffff)

(defstruct (bipartite-graph
            (:constructor make-bgraph
                (size1
                 size2
                 &aux
                 (graph1 (make-array size1 :element-type 'list :initial-element nil))
                 (matching1 (make-array size1 :element-type 'fixnum :initial-element -1))
                 (matching2 (make-array size2 :element-type 'fixnum :initial-element -1))))
            (:conc-name bgraph-))
  (size1 0 :type (unsigned-byte 32))
  (size2 0 :type (unsigned-byte 32))
  (graph1 nil :type (simple-array list (*)))
  (matching1 nil :type (simple-array fixnum (*)))
  (matching2 nil :type (simple-array fixnum (*))))

(declaim (inline bgraph-add-edge!))
(defun bgraph-add-edge! (bgraph vertex1 vertex2)
  (push vertex2 (aref (bgraph-graph1 bgraph) vertex1))
  bgraph)

(defun %fill-levels (bgraph levels1 levels2 queue)
  "Does BFS and fills LEVELS."
  (declare (optimize (speed 3) (safety 0))
           ((simple-array (unsigned-byte 32) (*)) levels1 levels2 queue))
  (let ((graph1 (bgraph-graph1 bgraph))
        (matching1 (bgraph-matching1 bgraph))
        (matching2 (bgraph-matching2 bgraph))
        (q-front 0)
        (q-end 0)
        (found nil))
    (declare ((integer 0 #.most-positive-fixnum) q-front q-end))
    (labels ((enqueue (obj)
               (setf (aref queue q-end) obj)
               (incf q-end))
             (dequeue ()
               (prog1 (aref queue q-front)
                 (incf q-front))))
      (declare (inline enqueue dequeue))
      (fill levels1 +graph-inf-distance+)
      (fill levels2 +graph-inf-distance+)
      (dotimes (i (bgraph-size1 bgraph))
        (when (= -1 (aref matching1 i))
          (setf (aref levels1 i) 0)
          (enqueue i)))
      (loop until (= q-front q-end)
            for vertex = (dequeue)
            do (dolist (next (aref graph1 vertex))
                 (when (= +graph-inf-distance+ (aref levels2 next))
                   (setf (aref levels2 next) (+ 1 (aref levels1 vertex)))
                   (let ((partner (aref matching2 next)))
                     (when (= -1 partner)
                       (setq found t)
                       (return))
                     (setf (aref levels1 partner) (+ 1 (aref levels2 next)))
                     (enqueue partner))))))
    found))

(defun %find-matching (bgraph src levels1 levels2)
  "Does DFS and makes matching greedily on the residual network."
  (declare (optimize (speed 3) (safety 0))
           ((integer 0 #.most-positive-fixnum) src)
           ((simple-array (unsigned-byte 32) (*)) levels1 levels2))
  (let ((matching1 (bgraph-matching1 bgraph))
        (matching2 (bgraph-matching2 bgraph))
        (graph1 (bgraph-graph1 bgraph)))
    (labels ((dfs (v)
               (declare ((integer 0 #.most-positive-fixnum) v))
               (dolist (next (aref graph1 v))
                 (when (= (aref levels2 next) (+ 1 (aref levels1 v)))
                   (setf (aref levels2 next) +graph-inf-distance+) ; mark visited
                   (let ((partner (aref matching2 next)))
                     (when (or (= -1 partner) (dfs partner))
                       (setf (aref matching1 v) next
                             (aref matching2 next) v
                             (aref levels1 v) +graph-inf-distance+ ; mark visited
                             )
                       (return-from dfs t)))))
               (setf (aref levels1 v) +graph-inf-distance+) ; mark visited
               nil ; not matched
               ))
      (dfs src))))

(declaim (ftype (function * (values (unsigned-byte 32) &optional)) bgraph-build-matching!))
(defun bgraph-build-matching! (bgraph)
  "Makes a maximum bipartite matching and returns two vectors: correspondence
from group 1 to group 2, and correspondence from group 2 to group 1. At an
unmatched vertex, -1 is stored."
  (declare (optimize (speed 3)))
  (let* ((size1 (bgraph-size1 bgraph))
         (size2 (bgraph-size2 bgraph))
         (matching1 (bgraph-matching1 bgraph))
         (levels1 (make-array size1 :element-type '(unsigned-byte 32)))
         (levels2 (make-array size2 :element-type '(unsigned-byte 32)))
         (queue (make-array (+ size1 size2) :element-type '(unsigned-byte 32)))
         (count 0))
    (declare ((integer 0 #.most-positive-fixnum) count))
    (loop while (%fill-levels bgraph levels1 levels2 queue)
          do (dotimes (v size1)
               (when (and (= -1 (aref matching1 v))
                          (%find-matching bgraph v levels1 levels2))
                 (incf count))))
    count))

(defun coerce-to-bgraph (graph)
  "Converts adjacency lists representation of undirected graph to
BIPARTITE-GRAPH.

GRAPH := vector of adjacency lists"
  (declare (vector graph))
  (let* ((n (length graph))
         (visited (make-array n :element-type 'bit :initial-element 0))
         (colors (make-array n :element-type 'bit :initial-element 0))
         (nums (make-array n :element-type 'fixnum))
         (size0 0)
         (size1 0))
    (declare ((integer 0 #.most-positive-fixnum) size0 size1))
    (labels ((dfs (vertex color)
               (cond ((zerop (aref visited vertex))
                      (setf (aref visited vertex) 1
                            (aref colors vertex) color)
                      (if (zerop color)
                          (setf (aref nums vertex) size0
                                size0 (+ size0 1))
                          (setf (aref nums vertex) size1
                                size1 (+ size1 1)))
                      (if (= color 1)
                          (dolist (neighbor (aref graph vertex))
                            (dfs neighbor 0))
                          (dolist (neighbor (aref graph vertex))
                            (dfs neighbor 1))))
                     ((/= color (aref colors vertex))
                      (error "Not bipartite.")))))
      (dotimes (i n)
        (when (zerop (aref visited i))
          (dfs i 1)))
      (let ((bgraph (make-bgraph size0 size1)))
        (dotimes (i n)
          (when (zerop (aref colors i))
            (let ((i-num (aref nums i)))
              (dolist (j (aref graph i))
                (let ((j-num (aref nums j)))
                  (bgraph-add-edge! bgraph i-num j-num))))))
        bgraph))))

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

;;;
;;; Queue with singly linked list
;;;

(defstruct (queue (:constructor make-queue
                      (&optional list &aux (tail (last list)))))
  (list nil :type list)
  (tail nil :type list))

(declaim (inline enqueue))
(defun enqueue (obj queue)
  "Pushes OBJ to the end of QUEUE."
  (symbol-macrolet ((list (queue-list queue))
                    (tail (queue-tail queue)))
    (if (null list)
        (setf tail (list obj)
              list tail)
        (setf (cdr tail) (list obj)
              tail (cdr tail))))
  queue)

(declaim (inline dequeue))
(defun dequeue (queue)
  "Removes and returns the element at the front of QUEUE. Returns NIL if QUEUE
is empty."
  (pop (queue-list queue)))

(declaim (inline queue-empty-p))
(defun queue-empty-p (queue)
  (null (queue-list queue)))

(declaim (inline queue-peek))
(defun queue-peek (queue)
  (car (queue-list queue)))

(declaim (inline enqueue-front))
(defun enqueue-front (obj queue)
  "Pushes OBJ to the front of QUEUE."
  (symbol-macrolet ((list (queue-list queue))
                    (tail (queue-tail queue)))
    (if (null list)
        (setf tail (list obj)
              list tail)
        (push obj list))
    queue))

(in-package :cl-user)

(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))
         (graph (make-array n :element-type 'list :initial-element nil)))
    (dotimes (i (- n 1))
      (let ((a (- (read-fixnum) 1))
            (b (- (read-fixnum) 1)))
        (push a (aref graph b))
        (push b (aref graph a))))
    (let* ((bgraph (coerce-to-bgraph graph))
           (res (bgraph-build-matching! bgraph)))
      (write-line
       (if (= (* res 2) n)
           "Second"
           "First")))))

#-swank (main)

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

#+swank
(defun io-equal (in-string out-string &key (function #'main) (test #'equal))
  "Passes IN-STRING to *STANDARD-INPUT*, executes FUNCTION, and returns true if
the string output to *STANDARD-OUTPUT* is equal to OUT-STRING."
  (labels ((ensure-last-lf (s)
             (if (eql (uiop:last-char s) #\Linefeed)
                 s
                 (uiop:strcat s uiop:+lf+))))
    (funcall test
             (ensure-last-lf out-string)
             (with-output-to-string (out)
               (let ((*standard-output* out))
                 (with-input-from-string (*standard-input* (ensure-last-lf in-string))
                   (funcall function)))))))

#+swank
(defun get-clipbrd ()
  (with-output-to-string (out)
    (run-program "powershell.exe" '("-Command" "Get-Clipboard") :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* out))
    (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))))))

#+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)))

;; To run: (5am:run! :sample)
#+swank
(it.bese.fiveam:test :sample
  (it.bese.fiveam:is
   (common-lisp-user::io-equal "3
1 2
2 3
"
    "First
"))
  (it.bese.fiveam:is
   (common-lisp-user::io-equal "4
1 2
2 3
2 4
"
    "First
"))
  (it.bese.fiveam:is
   (common-lisp-user::io-equal "6
1 2
2 3
3 4
2 5
5 6
"
    "Second
")))