Public Class Program
  Shared Sub Main()
    Dim nd As Integer() = Array.ConvertAll(Of String, Integer)(Console.ReadLine().Split(" "), AddressOf Integer.Parse)
    Dim n As Integer = nd(0)
    dim d As Integer = nd(1)
    Dim output As Long = Math.Ceiling(n / (d * 2 + 1))
    Console.WriteLine(output.ToString())
  End Sub
End Class