require 'pp'

n = gets.to_i
v = gets.strip.split.map(&:to_i)
dp = {}

dp[0] = v[0]
dp[1] = [v[0], v[1]].max

if n > 1
  (2..n - 1).each do |i|
    dp[i] = [dp[i - 1], dp[i - 2] + v[i]].max
  end
end

puts dp[n - 1]