let () =
  let n = Scanf.scanf "%d " (fun i -> i) in
  let s = Array.init n (fun _ -> Scanf.scanf "%s " (fun i -> i)) in
  let rec doit i =
    if i = n then assert false
    else
      let t = Scanf.scanf "%s " (fun i -> i) in
      if s.(i) <> t then (i, t)
      else doit (i + 1) in
  let (i, t) = doit 0 in
  Printf.printf "%d\n%s\n%s\n" (i + 1) s.(i) t