// 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)

// 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))