using System; using System.Collections.Generic; using System.Linq; using System.IO; using System.Threading; using System.Runtime.CompilerServices; using System.Text; using System.Diagnostics; using System.Numerics; using static System.Console; using static System.Convert; using static System.Math; using static Template; using SC = Scanner; public partial class Solver { int N, M; public void Solve() { sc.ArrInt.Out(out N, out M); int[] L = new int[N], R = new int[N]; var ts = new TwoSat(N); for (int i = 0; i < N; i++) { sc.ArrInt.Out(out L[i], out R[i]); L[i]--;R[i]--; if (i > 0) { if (inter(L[i - 1], R[i - 1], L[i], R[i])) { ts.AddClosure(i - 1, false, i, false); } rev(ref L[i - 1], ref R[i - 1]); if (inter(L[i - 1], R[i - 1], L[i], R[i])) { ts.AddClosure(i - 1, true, i, false); } rev(ref L[i], ref R[i]); if (inter(L[i - 1], R[i - 1], L[i], R[i])) { ts.AddClosure(i - 1, true, i, true); } rev(ref L[i - 1], ref R[i - 1]); if (inter(L[i - 1], R[i - 1], L[i], R[i])) { ts.AddClosure(i - 1, false, i, true); } rev(ref L[i], ref R[i]); } } if (ts.Execute()) Console.WriteLine("YES"); else Console.WriteLine("NO"); } bool inter(int l1, int r1, int l2, int r2) => !(Max(l1, l2) > Min(r1, r2)); void rev(ref int l,ref int r) { int t = r; r = M - 1 - l; l = M - 1 - t; } } class TwoSat { StronglyConnectedComponents scc; public bool[] Answer { get; private set; } public TwoSat(int N) { scc = new StronglyConnectedComponents(N << 1); Answer = new bool[N]; } //(x_i=f)V(x_j=g) <-> !(x_i=f)->(x_j=g) <-> !(x_j=g)->(x_i=f)の追加 public void AddClosure(int i, bool f, int j, bool g) { scc.AddEdge((i << 1) | (f ? 0 : 1), (j << 1) | (g ? 1 : 0)); scc.AddEdge((j << 1) | (g ? 0 : 1), (i << 1) | (f ? 1 : 0)); } public bool Execute() { scc.Execute(); var gp = scc.Group; var len = gp.Length >> 1; for (int i = 0; i < len; i++) { if (gp[i << 1] == gp[(i << 1) | 1]) return false; Answer[i] = gp[i << 1] < gp[(i << 1) | 1];//DAG } return true; } } public class StronglyConnectedComponents { int size; List edges; private int[][] scc; public int Count { get; private set; } public int[] Group { get; private set; } public int[] GroupAt(int k) => scc[k]; public StronglyConnectedComponents(int count) { size = count; edges = new List(); } public void AddEdge(int from, int to) { edges.Add(new Edge(from, to)); } /// /// O(V+E) /// /// scc[i]:i番目の強連結成分の頂点 public int[][] Execute() { //e.fromでe.toをソート var start = new int[size + 1]; var toList = new int[edges.Count]; foreach (var e in edges) start[e.from + 1]++; for (int i = 0; i < start.Length - 1; i++) start[i + 1] += start[i]; var count = start.ToArray(); foreach (var e in edges) toList[count[e.from]++] = e.to; //lowlink int nowOrd = 0; int[] low = new int[size], ord = new int[size]; Group = new int[size]; var stack = new Stack(size); for (int i = 0; i < ord.Length; i++) ord[i] = -1; Action dfs = null; dfs = v => { low[v] = ord[v] = nowOrd++; stack.Push(v); for (int i = start[v]; i < start[v + 1]; i++) { var to = toList[i]; if (ord[to] == -1) { dfs(to); low[v] = Min(low[v], low[to]); } else low[v] = Min(low[v], ord[to]); } if (low[v] == ord[v]) { while (true) { var u = stack.Pop(); ord[u] = size; Group[u] = Count; if (u == v) break; } Count++; } }; for (int i = 0; i < ord.Length; i++) { if (ord[i] == -1) dfs(i); } for (int i = 0; i < Group.Length; i++) { Group[i] = Count - 1 - Group[i]; count[i] = 0; } scc = new int[Count][]; foreach (var g in Group) count[g]++; for (int i = 0; i < scc.Length; i++) scc[i] = new int[count[i]]; for (int i = 0; i < Group.Length; i++) scc[Group[i]][--count[Group[i]]] = i; return scc; } struct Edge { public int from, to; public Edge(int f, int t) { from = f; to = t; } } } #region Template public partial class Solver { public SC sc = new SC(); static void Main(string[] args) { Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false }); var sol = new Solver(); int testcase = 1; //testcase = sol.sc.Int; //var th = new Thread(sol.Solve, 1 << 26);th.Start();th.Join(); while (testcase-- > 0) sol.Solve(); Console.Out.Flush(); } } public static class Template { [MethodImpl(MethodImplOptions.AggressiveInlining)] public static bool chmin(ref T a, T b) where T : IComparable { if (a.CompareTo(b) > 0) { a = b; return true; } return false; } [MethodImpl(MethodImplOptions.AggressiveInlining)] public static bool chmax(ref T a, T b) where T : IComparable { if (a.CompareTo(b) < 0) { a = b; return true; } return false; } [MethodImpl(MethodImplOptions.AggressiveInlining)] public static void swap(ref T a, ref T b) { var t = b; b = a; a = t; } [MethodImpl(MethodImplOptions.AggressiveInlining)] public static void swap(this IList A, int i, int j) { var t = A[i]; A[i] = A[j]; A[j] = t; } public static T[] Create(int n, Func f) { var rt = new T[n]; for (var i = 0; i < rt.Length; ++i) rt[i] = f(); return rt; } public static T[] Create(int n, Func f) { var rt = new T[n]; for (var i = 0; i < rt.Length; ++i) rt[i] = f(i); return rt; } public static void Out(this IList A, out T a) => a = A[0]; public static void Out(this IList A, out T a, out T b) { a = A[0]; b = A[1]; } public static void Out(this IList A, out T a, out T b, out T c) { A.Out(out a, out b); c = A[2]; } public static void Out(this IList A, out T a, out T b, out T c, out T d) { A.Out(out a, out b, out c); d = A[3]; } public static string Concat(this IEnumerable A, string sp) => string.Join(sp, A); public static char ToChar(this int s, char begin = '0') => (char)(s + begin); public static IEnumerable Shuffle(this IEnumerable A) => A.OrderBy(v => Guid.NewGuid()); public static int CompareTo(this T[] A, T[] B, Comparison cmp = null) { cmp = cmp ?? Comparer.Default.Compare; for (var i = 0; i < Min(A.Length, B.Length); i++) { int c = cmp(A[i], B[i]); if (c > 0) return 1; else if (c < 0) return -1; } if (A.Length == B.Length) return 0; if (A.Length > B.Length) return 1; else return -1; } public static string ToStr(this T[][] A) => A.Select(a => a.Concat(" ")).Concat("\n"); public static int ArgMax(this IList A, Comparison cmp = null) { cmp = cmp ?? Comparer.Default.Compare; T max = A[0]; int rt = 0; for (int i = 1; i < A.Count; i++) if (cmp(max, A[i]) < 0) { max = A[i]; rt = i; } return rt; } public static T PopBack(this List A) { var v = A[A.Count - 1]; A.RemoveAt(A.Count - 1); return v; } public static void Fail(T s) { Console.WriteLine(s); Console.Out.Close(); Environment.Exit(0); } } public class Scanner { public string Str => Console.ReadLine().Trim(); public int Int => int.Parse(Str); public long Long => long.Parse(Str); public double Double => double.Parse(Str); public int[] ArrInt => Str.Split(' ').Select(int.Parse).ToArray(); public long[] ArrLong => Str.Split(' ').Select(long.Parse).ToArray(); public char[][] Grid(int n) => Create(n, () => Str.ToCharArray()); public int[] ArrInt1D(int n) => Create(n, () => Int); public long[] ArrLong1D(int n) => Create(n, () => Long); public int[][] ArrInt2D(int n) => Create(n, () => ArrInt); public long[][] ArrLong2D(int n) => Create(n, () => ArrLong); private Queue q = new Queue(); [MethodImpl(MethodImplOptions.AggressiveInlining)] public T Next() { if (q.Count == 0) foreach (var item in Str.Split(' ')) q.Enqueue(item); return (T)Convert.ChangeType(q.Dequeue(), typeof(T)); } public void Make(out T1 v1) => v1 = Next(); public void Make(out T1 v1, out T2 v2) { v1 = Next(); v2 = Next(); } public void Make(out T1 v1, out T2 v2, out T3 v3) { Make(out v1, out v2); v3 = Next(); } public void Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4) { Make(out v1, out v2, out v3); v4 = Next(); } public void Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5) { Make(out v1, out v2, out v3, out v4); v5 = Next(); } public void Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5, out T6 v6) { Make(out v1, out v2, out v3, out v4, out v5); v6 = Next(); } public void Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5, out T6 v6, out T7 v7) { Make(out v1, out v2, out v3, out v4, out v5, out v6); v7 = Next(); } public (T1, T2) Make() { Make(out T1 v1, out T2 v2); return (v1, v2); } public (T1, T2, T3) Make() { Make(out T1 v1, out T2 v2, out T3 v3); return (v1, v2, v3); } public (T1, T2, T3, T4) Make() { Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4); return (v1, v2, v3, v4); } } #endregion