open System

let solve n =  
  let dp = Array.zeroCreate (n + 1)  
  dp.[n] <- 1
  for i in n .. -1 .. 0 do
    if i + 2 <= n then
      dp.[i] <- dp.[i] + dp.[i + 2]      
    if i + 1 <= n then
      dp.[i] <- dp.[i] + dp.[i + 1]              
  dp.[0]
  
let N = Console.ReadLine() |> int

solve N
|> Console.WriteLine