let calc a =
    let a_sorted = Array.append (Array.sort a) [| 0 |]
    let index = [| 1 .. a_sorted.Length - 1 |]
    (Array.filter (fun i -> a_sorted.[i] - a_sorted.[i - 1] = 1) index).Length + 1

let main =
    let n = stdin.ReadLine() |> int

    let e =
        [| for i = 0 to n - 1 do
               stdin.ReadLine() |> int |]

    printfn "%d" (calc e)
    0