Scanf.scanf "%s" (fun s ->
    let n = String.length s in
    let rec loop i t r e =
        if i = n then min (e / 2) (min t r) else
            if s.[i] = 't' then loop (i + 1) (t + 1) r e else
            if s.[i] = 'r' then loop (i + 1) t (r + 1) e else
            if s.[i] = 'e' then loop (i + 1) t r (e + 1) else
                                loop (i + 1) t r e
    in
    loop 0 0 0 0 |> Printf.printf "%d\n"
)