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