
open Scanf
open Printf

let flip f x y = f y x

let rec range a b = if a >= b then [] else a :: range (a+1) b

let read_int () = scanf " %d" (fun x -> x)
let rec read_ints n = if n = 0 then [] else let i = read_int () in i :: read_ints (n-1)

let rec for_iter a b f = if a >= b then [] else let x = f a in x :: for_iter (a+1) b f
let rec for_iter_ a b f = if a >= b then () else (f a; for_iter_ (a+1) b f)

let () =
  let s = read_line () in
  range 0 (String.length s) 
  |> List.map (fun i -> (i, s.[i]))
  |> List.filter (fun (i, _) -> i mod 2 = 0)
  |> List.map snd
  |> List.iter (printf "%c");
  printf "\n"
