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")

  def main do
    s = input()
    n = String.length(s)

    if rem(n, 2) == 1 do
      false
    else
      m = div(n, 2)
      a = String.slice(s, 0, m)
      b = String.slice(s, m, n)
      a == b
    end
    |> then(fn b -> if b, do: "YES", else: "NO" end)
    |> IO.puts
  end
end