let rec loop(start, last) =
    let mid = (start + last) / 2
    printfn "Is your number %d (H - Too High/L - Too Low/=)?" mid
    let answer = System.Console.ReadLine()
    match answer with
    | "H" -> loop(start, mid)
    | "L" -> loop(mid+1, last)
    | "=" -> printfn "Your number is %d!" mid

loop(0, 100)