n = gets.to_i

A = [0] + gets.split.map(&:to_i)

d = Array.new(n + 1) { [0] * 2 }

d[0][0] = 0

d[0][1] = -Float::INFINITY

for i in (1..n)

  d[i][0] = [d[i - 1][0], d[i - 1][1]].max

  d[i][1] = d[i - 1][0] + A[i]

end

ans = d[n].max

puts ans