let () =
  Scanf.scanf "%d\n" @@ fun n ->
  let ans = Array.init n @@ fun _ -> Scanf.scanf "%d:%d %d:%d\n" @@ fun h1 m1 h2 m2 ->
    let h = ref (if h1 > h2 then h2 + 24 - h1 else h2 - h1) in
    let m = if m2 - m1 < 0 then (h := !h - 1; m2 + 60 - m1) else m2 - m1 in
    (!h) * 60 + m in
  Printf.printf "%d\n" (Array.fold_left (+) 0 ans)