n = gets.to_i
v = gets.split.map(&:to_i)
dp = Array.new(n){0}
dp[0] = v[0]
if n >= 2
  dp[1] = [dp[0], v[1]].max
  if n >= 3
    (2...n).each do |i|
      dp[i] = [dp[i-3]+v[i], dp[i-2]+v[i], dp[i-1]].max
    end
  end
end
p dp[n-1]