$n = gets.to_i
$v = gets.strip.split.map{|e| e.to_i}

$dp = {}
$n.times {|i| $dp[i] = {}}

def recursive i, now
  if i >= $n
    return now
  end
  if $dp[i].key?(now)
    return $dp[i][now]
  end
  # 今回の皿を取る場合
  a = recursive(i + 2, now + $v[i])
  # 見送る場合
  b = recursive(i + 1, now)
  max = [a, b].max
  $dp[i][now] = max
end

puts recursive 0, 0