Scanf.scanf "%d" (fun n ->
    let module S = Set.Make (struct type t = char let compare = compare end) in
    let rec loop i set =
        if i = n then S.cardinal set else
            let set = Scanf.scanf " %c" (fun c -> S.add c set) in
            loop (i + 1) set
    in
    let ans = loop 0 S.empty in
    print_endline @@ if ans = 3 then "Three" else "Four"
)