// Modules
open System

// Recursive definition of Fibonacci numbers
let rec fib n =
    match n with
    | 0 -> 0
    | 1 -> 1
    | _ -> fib (n-1) + fib (n-2)

let rec fibSmart n =
  match n with
  | n when n < 0 -> failwith (sprintf "Error: %d is less than 0" n)
  | (0|1) -> n
  | _ -> fibSmart (n-1) + fibSmart (n-2)

// Read from stdin and print result
printfn "Inserisci l'indice del numero di fibonacci che vuoi calcolare:\n"
let i = Console.ReadLine() |> int
printfn "%A" (fib (i))
printfn "%A" (fibSmart (i))