class Yukicoder
  def initialize
    n = gets.to_i
    v = gets.chomp.split.map(&:to_i)

    dp = Array.new(n, 0)
    dp[0] = v[0]
    dp[1] = v[1] || 0

    2.upto(n-1) do |i|
      dp[i] = dp[0..i-2].max + v[i]
    end

    puts dp.max
  end
end

Yukicoder.new