require 'pp'

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

if n === 1
  puts v[0]
  exit
end

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]