N = gets.to_i
V = gets.split.map(&:to_i)
$dp = {}
def f(v ,i)
  $dp[i] ||= if i < 1
    V[i]
  elsif i < 2
    [V[i], V[i - 1]].max
  else
    [V[i] + f(v, i-2), f(v, i - 1)].max
  end
end

p f(0, N-1)