using System; using System.IO; using System.Linq; using System.Text; using System.Diagnostics; using System.Collections.Generic; using System.Text.RegularExpressions; using Enu = System.Linq.Enumerable; class Program { void Solve() { int L = reader.Int(), K = reader.Int(); Console.WriteLine((L - 1) / (2 * K) * K); } Reader reader = new Reader(Console.In); static void Main() { new Program().Solve(); } } class Reader { private readonly TextReader reader; private readonly char[] separator = { ' ' }; private readonly StringSplitOptions removeOp = StringSplitOptions.RemoveEmptyEntries; private string[] A = new string[0]; private int i; public Reader(TextReader r) { reader = r; } public Reader(string file) { reader = new StreamReader(file); } public bool HasNext() { return Enqueue(); } public string String() { return Dequeue(); } public int Int() { return int.Parse(Dequeue()); } public long Long() { return long.Parse(Dequeue()); } public double Double() { return double.Parse(Dequeue()); } public int[] IntLine() { var s = Line(); return s == "" ? new int[0] : Array.ConvertAll(Split(s), int.Parse); } public int[] IntArray(int N) { return Enu.Range(0, N).Select(i => Int()).ToArray(); } public int[][] IntGrid(int H) { return Enu.Range(0, H).Select(i => IntLine()).ToArray(); } public string[] StringArray(int N) { return Enu.Range(0, N).Select(i => Line()).ToArray(); } public string Line() { return reader.ReadLine().Trim(); } private string[] Split(string s) { return s.Split(separator, removeOp); } private bool Enqueue() { if (i < A.Length) return true; string line = reader.ReadLine(); if (line == null) return false; if (line == "") return Enqueue(); A = Split(line); i = 0; return true; } private string Dequeue() { Enqueue(); return A[i++]; } }