require 'pp'

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

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

puts dp[n - 1]