let () =
  let o,e = Scanf.scanf "%s %s " (fun a b -> a,b) in
  let o = Batteries.String.to_list o in
  let e = Batteries.String.to_list e in

  let rec aux l1 l2 res =
    match l1,l2 with
    | (hd1 :: tl1), (hd2 :: tl2) -> aux tl1 tl2 (res @ [hd1;hd2])
    | (hd1 :: tl1), [] -> res @ [hd1]
    | [], [] -> res
  in

  Printf.printf "%s\n" @@
  Batteries.String.of_list (aux o e [])

