let () =
  Scanf.scanf "%s" (fun s ->
      let len = String.length s in
      let rec f i =
        match i mod 2 = 0 with
        | _ when i > len -> ()
        | true ->
            print_char s.[i] ;
            f (i + 1)
        | false -> f (i + 1)
      in
      f 0 ; print_newline () )
