using System; using System.Collections; using System.Collections.Generic; using System.IO; using System.Linq; class Program { static void Main(string[] args) { var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false }; Console.SetOut(sw); Solve(); Console.Out.Flush(); } static void Solve() { var N = sc.ReadInt(); var K = sc.ReadInt(); var G = new List[N]; for (int i = 0; i < N; i++) { G[i] = new List(); } for (int i = 0; i < N - 1; i++) { var a = sc.ReadInt(); var b = sc.ReadInt(); a--; b--; G[a].Add(b); G[b].Add(a); } if (K > N) { Console.WriteLine(-1); } else { Console.WriteLine(K - 1); } } static Scanner sc = new Scanner(); } class Scanner { string[] S = new string[0]; int Index = 0; char[] Separators = new char[] { ' ' }; public string Next() { if (this.Index < this.S.Length) return this.S[this.Index++]; var line = ""; while (line == "") line = Console.ReadLine(); this.S = line.Split(this.Separators, StringSplitOptions.RemoveEmptyEntries); if (this.S.Length == 0) return this.Next(); this.Index = 0; return this.S[this.Index++]; } public string ReadStr() { return this.Next(); } public char ReadChar() { return this.Next()[0]; } public int ReadInt() { return int.Parse(this.Next()); } public uint ReadUInt() { return uint.Parse(this.Next()); } public long ReadLong() { return long.Parse(this.Next()); } public double ReadDouble() { return double.Parse(this.Next()); } public Tuple ReadTup(int add = 0) { return Tuple.Create(this.ReadInt() + add, this.ReadInt() + add); } public Tuple ReadTupLong(int add = 0) { return Tuple.Create(this.ReadLong() + add, this.ReadLong() + add); } public Tuple ReadTup3(int add = 0) { return Tuple.Create(this.ReadInt() + add, this.ReadInt() + add, this.ReadInt() + add); } public Tuple ReadTup4(int add = 0) { return Tuple.Create(this.ReadInt() + add, this.ReadInt() + add, this.ReadInt() + add, this.ReadInt() + add); } public int[] ReadIntArray(int n) { var array = new int[n]; for (int i = 0; i < array.Length; i++) { array[i] = this.ReadInt(); } return array; } public long[] ReadLongArray(int n) { var array = new long[n]; for (int i = 0; i < array.Length; i++) { array[i] = this.ReadLong(); } return array; } public double[] ReadDoubleArray(int n) { var array = new double[n]; for (int i = 0; i < array.Length; i++) { array[i] = this.ReadDouble(); } return array; } public char[] ReadCharArray(int n) { var array = new char[n]; for (int i = 0; i < array.Length; i++) { array[i] = this.ReadChar(); } return array; } public string[] ReadStrArray(int n) { var array = new string[n]; for (int i = 0; i < array.Length; i++) { array[i] = this.ReadStr(); } return array; } public Tuple[] ReadTupLongArray(int n, int add = 0) { var array = new Tuple[n]; for (int i = 0; i < n; i++) { array[i] = this.ReadTupLong(add); } return array; } public Tuple[] ReadTupArray(int n, int add = 0) { var array = new Tuple[n]; for (int i = 0; i < n; i++) { array[i] = this.ReadTup(add); } return array; } public Tuple[] ReadTup3Array(int n, int add = 0) { var array = new Tuple[n]; for (int i = 0; i < n; i++) { array[i] = this.ReadTup3(add); } return array; } public Tuple[] ReadTup4Array(int n, int add = 0) { var array = new Tuple[n]; for (int i = 0; i < n; i++) { array[i] = this.ReadTup4(add); } return array; } }