N = gets.to_i
V = gets.chomp.split.map(&:to_i)

dp = Array.new(V.length, 0)
if N == 1
  puts V[0]
  return
end

dp[0] = V[0]
dp[1] = (V[0] < V[1])? V[1] : V[0]

2.upto(V.length-1) do |i|
  dp[i] = [dp[i-2] + V[i], dp[i-1]].max
end

puts dp[-1]