let f x = x mod (1000000000 + 7)

let () =
  let n = Scanf.scanf "%d " (fun i -> i) in
  let rec doit i acc =
    if i = n then acc
    else
      let c, d = Scanf.scanf "%d %d " (fun c d -> c, d) in
      let m = (c + 1) / 2 in
      doit (i + 1) (acc + (f m) * (f d) |> f) in
  doit 0 0 |> Printf.printf "%d\n"