defmodule Main do
  def input, do: IO.read(:line) |> String.trim
  def ii, do: input() |> String.to_integer
  def li, do: input() |> String.split |> Enum.map(&String.to_integer/1)
  def yn(b), do: IO.puts(if b, do: "Yes", else: "No")

  @mod 10**9 + 7

  def f([x]), do: x
  def f(xs) do
    Enum.chunk_every(xs, 2, 1, :discard)
    |> Enum.map(fn [a, b] -> rem(a+b, @mod) end)
    |> f()
  end

  def main do
    n = ii()
    a = li()

    ans = f(a)
    IO.puts ans
  end
end