using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace ProgrammingContest { class MainClass : IDisposable { Scanner sc; Writer wr; string backPath = ".."; char dirSep = System.IO.Path.DirectorySeparatorChar; string inFilePath = null; string outFilePath = null; public MainClass() { this.inFilePath = this.backPath + this.dirSep + this.backPath + this.dirSep + "in.txt"; this.outFilePath = this.backPath + this.dirSep + this.backPath + this.dirSep + "out.txt"; } static void Main(string[] args) { using (var mainClass = new MainClass()) { //mainClass.MakeTestCase(); mainClass.Solve(); } } public void Dispose() { if (this.sc != null) { this.sc.Dispose(); this.sc = null; } if (this.wr != null) { this.wr.Dispose(); this.wr = null; } } void MakeTestCase() { Random rand = new Random(); this.wr = new Writer(inFilePath); } void Solve() { this.wr = new Writer(this.isReactive); //this.wr = new Writer(this.outFilePath); #if DEBUG if (!this.isReactive) this.sc = new Scanner(this.inFilePath); else this.sc = new Scanner(); #else this.sc = new Scanner(); #endif int N = sc.NextInt; int M = sc.NextInt; UnionFind uf = new UnionFind(N); List[] G = new List[N].Select(e => new List()).ToArray(); for (int i = 0; i < M; i++) { int a = sc.NextInt; int b = sc.NextInt; G[a].Add(b); G[b].Add(a); uf.Unite(a, b); } int odd = 0; for (int i = 0; i < N; i++) { odd += G[i].Count % 2; } HashSet set = new HashSet(); int cnt = 0; for (int i = 0; i < N; i++) { if (!set.Contains(uf.Find(i))) { set.Add(uf.Find(i)); if (uf.Count(i) > 1) { cnt++; } } } wr.WriteLine((odd == 0 || odd == 2) && cnt <= 1 ? "YES" : "NO"); } bool isReactive = false; // TODO: reactive check !! } class UnionFind { private int[] uni; int count_; public UnionFind(int n) { this.uni = new int[n]; for (int i = 0; i < n; i++) { this.uni[i] = -1; } } public int Count() { return this.count_; } public int Count(int n) { return -this.uni[this.Find(n)]; } public int Find(int n) { return (this.uni[n] < 0 ? n : this.uni[n] = this.Find(this.uni[n])); } public bool Unite(int a, int b) { a = this.Find(a); b = this.Find(b); if (a == b) { return false; } if (this.uni[a] > this.uni[b]) { int t = a; a = b; b = t; } this.uni[a] += this.uni[b]; this.uni[b] = a; this.count_--; return true; } public bool Same(int a, int b) { return this.Find(a) == this.Find(b); } } class Writer : IDisposable { private System.IO.TextWriter writer; private StringBuilder sb; private bool isReactive; public Writer(string path) : this(new System.IO.StreamWriter(path)) { } public Writer(bool isReactive) : this(null, isReactive) { } public Writer(System.IO.TextWriter writer = null, bool isReactive = false) { this.writer = (writer ?? Console.Out); this.isReactive = isReactive; if (!this.isReactive) this.sb = new StringBuilder(); } public void Dispose() { if (!this.isReactive) this.writer.Write(sb.ToString()); if (!this.writer.Equals(Console.Out)) this.writer.Dispose(); } public void Write(object val) { if (this.isReactive) { this.writer.Write(val.ToString()); this.writer.Flush(); } else this.sb.Append(val.ToString()); } public void Write(string format, params object[] vals) { if (this.isReactive) { this.writer.Write(format, vals); this.writer.Flush(); } else this.sb.AppendFormat(format, vals); } public void WriteLine(object val) { this.Write(val.ToString() + System.Environment.NewLine); } public void WriteLine(string format, params object[] vals) { this.Write(format + System.Environment.NewLine, vals); } } class Scanner : IDisposable { private Queue buffer; private char[] sep; private System.IO.TextReader reader; public Scanner(string path) : this(new System.IO.StreamReader(path)) { } public Scanner(System.IO.TextReader reader = null) { this.buffer = new Queue(); this.sep = new char[] { ' ' }; this.reader = (reader ?? Console.In); } private void CheckBuffer() { if (this.buffer.Count == 0) { string str = string.Empty; while (string.IsNullOrEmpty(str)) str = this.reader.ReadLine(); str.Split(this.sep).ToList() .ForEach(el => this.buffer.Enqueue(el)); } } public void Dispose() { if (!this.reader.Equals(Console.In)) this.reader.Dispose(); } public string Next { get { this.CheckBuffer(); return this.buffer.Dequeue(); } } public int NextInt { get { return int.Parse(this.Next); } } public double NextDouble { get { return double.Parse(this.Next); } } public long NextLong { get { return long.Parse(this.Next); } } public bool IsEnd { get { this.CheckBuffer(); return this.buffer.Count == 0; } } } }