open System

let rec sumupto n = if n=0 then 0 else n + sumupto (n-1)
let rec factorial n = if n=0 then 1 else n * factorial (n-1)
let div n : float = float (sumupto n)/float (factorial n)

let read() =
    printfn "Please enter a number."
    System.Console.ReadLine()
let convert (source : string) =
    try System.Int32.Parse(source)
    with :? System.FormatException ->
        printfn "'%s' is not a number!" source;
        exit 1

let num1 : int = read() |> convert

printfn "result=%f" ( div num1 )

Console.ReadLine()