$n = gets.to_i - 1
$v = gets.split.map(&:to_i)
$dp = Array.new($n+1, -1)

def dfs(n)
  return $dp[0] = $v[0] if n == 0
  return $dp[1] = $v[1] if n == 1

  $dp[n] = $v[n] + (0..(n-2)).map {|i| ($dp[i] < 0 ? dfs(i) : $dp[i])}.max

  return $dp[n]
end

puts [dfs($n), ($n-1 > 0 ? dfs($n-1) : -1)].max