Imports System
Public Class B200
    Public Shared Sub Main()
        Dim N As Long
        N = Console.ReadLine()
        Dim L(N) As Long
        L(0) = 2
        L(1) = 1
        For i As Integer = 2 To N
            L(i) = L(i - 1) + L(i - 2)
        Next i
        Console.WriteLine(L(N))
    End Sub
End Class
