let N = stdin.ReadLine() |> int
let A = stdin.ReadLine().Split() |> Array.map int |> Array.toList

let rec loop i items count =
    match items with
    | [head] -> if head = i then count+1 else count
    | head :: [tail] -> if head = i then loop (i+1) [head] (count+1) else loop (i+1) [tail] count
    | head :: sec :: tail -> if i = head then loop (i+1) (head::tail) (count+1) 
                             else loop (i+1) (sec::tail) count

loop 1 A 0 |> stdout.WriteLine