n = gets.to_i
v = gets.split.map(&:to_i)
dp = Array.new(n + 1)
dp[0] = 0
dp[1] = v[0]
2.upto(n) do |i|
  dp[i] = [dp[i-2] + v[i-1], dp[i-1]].max
end
puts dp[n]