let stream_map f stream =
  Stream.from (fun _ -> try Some (f (Stream.next stream))
                        with Stream.Failure -> None)

let stream_fold f stream init =
  let result = ref init in
  Stream.iter (fun x -> result := f !result x) stream;
  !result



let solve hm_st =
  let calc_min (h1, m1, h2, m2) =
    (h2 * 60 + m2 + 1440 - (h1 * 60 + m1)) mod 1440
  in
  let min_st = stream_map calc_min hm_st in
  stream_fold ( + ) min_st 0

let read_hm n =
  Stream.from (fun i ->
    if i >= n then None
    else
      let h1, m1, h2, m2 = ref 0, ref 0, ref 0, ref 0 in
      Scanf.scanf
        "%d:%d %d:%d\n"
        (fun d1 d2 d3 d4 -> h1 := d1; m1 := d2; h2 := d3; m2 := d4);
      Some(!h1, !m1, !h2, !m2)
  )

let () =
  let n = read_line () |> int_of_string in
  let hm_st = read_hm n in
  solve hm_st |> string_of_int |> print_endline