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

;; BEGIN_INSERTED_CONTENTS
(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 (ftype (function * (values fixnum &optional)) read-fixnum))
(defun read-fixnum (&optional (in *standard-input*))
  (declare #.OPT
           #-swank (sb-kernel:ansi-stream in))
  (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))))))))

;;;
;;; Strongly connected components of directed graph
;;;

(defun make-scc (graph)
  "GRAPH := vector of adjacency lists"
  (declare #.OPT
           ((simple-array list (*)) graph))
  (let* ((n (length graph))
         (ords (make-array n :element-type 'uint31 :initial-element 0))
         (lows (make-array n :element-type 'uint31 :initial-element 0))
         (components (make-array n :element-type 'uint31))
         (stack (make-array n :element-type 'uint31))
         (in-stack (make-array n :element-type 'bit :initial-element 0))
         (time 0)
         (ord 0)
         (pointer 0))
    (declare (uint31 time ord pointer))
    (labels ((visit (v)
               (incf time)
               (setf (aref lows v) time
                     (aref ords v) time)
               (setf (aref stack pointer) v)
               (incf pointer)
               (setf (aref in-stack v) 1)
               (dolist (neighbor (aref graph v))
                 (cond ((zerop (aref ords neighbor))
                        (visit neighbor)
                        (setf (aref lows v)
                              (min (aref lows v) (aref lows neighbor))))
                       ((= 1 (aref in-stack neighbor))
                        (setf (aref lows v)
                              (min (aref lows v) (aref ords neighbor))))))
               (when (= (aref lows v) (aref ords v))
                 (loop
                   (decf pointer)
                   (let ((w (aref stack pointer)))
                     (setf (aref in-stack w) 0)
                     (setf (aref components w) ord)
                     (when (= v w)
                       (return))))
                 (incf ord))))
      (dotimes (v n)
        (when (zerop (aref ords v))
          (visit v)))
      components)))

(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)))

;;;
;;; Body
;;;

(defun main ()
  (declare #.OPT)
  (let* ((n (read))
         (m (read))
         (ls (make-array (* 2 n) :element-type 'uint16))
         (rs (make-array (* 2 n) :element-type 'uint16))
         (graph (make-array (* 4 n) :element-type 'list :initial-element nil))
         (2n (* 2 n))
         (4n (* 4 n)))
    (declare (uint16 n m))
    (dotimes (i n)
      (let* ((l (read-fixnum))
             (r (read-fixnum)))
        (declare (uint16 l r))
        (setf (aref ls i) l
              (aref rs i) r
              (aref ls (+ i n)) (- m r 1)
              (aref rs (+ i n)) (- m l 1))))
    (labels ((negate (x)
               (declare (uint16 x))
               (let ((res (+ x 2n)))
                 (if (>= res 4n)
                     (- res 4n)
                     res)))
             (add-clause! (literal1 literal2)
               (declare (uint16 literal1 literal2))
               (push (negate literal2) (aref graph literal1))
               (push (negate literal1) (aref graph literal2))))
      (declare (inline negate))
      (dotimes (x 2n)
        (loop for y from (+ x 1) below 2n
              do (when (and (/= (+ x n) y)
                            (not (or (< (aref rs x) (aref ls y))
                                     (< (aref rs y) (aref ls x)))))
                   (add-clause! x y))))
      (dotimes (x n)
        (add-clause! (negate x) (negate (+ x n)))
        (add-clause! x (+ x n)))
      (let* ((comps (make-scc graph)))
        (declare ((simple-array uint31 (*)) comps))
        (write-line
         (if (loop for x below 2n
                   thereis (= (aref comps x)
                              (aref comps (+ x 2n))))
             "NO"
             "YES"))))))

#-swank (main)