let ln2 = log 2.

let cookie nf =
  let ln = (log nf) /. ln2 in
  let f, c = floor ln, ceil ln in
  let ln0 = if ln -. f < c -. ln then f else c in
  if abs_float (nf -. 2. ** ln0) < 0.0000000001 then
    ln
  else ln +. 1.
let () = print_int @@ int_of_float @@ cookie @@ read_float ()