def inp(m=0) a=gets.chomp.split(" ").map(&:to_i);(a.size<2)? (m==0)? a[0]:a:a end
def copy(a) Marshal.load(Marshal.dump(a)) end
def kaizyo(n)(n < 2)? 1 : (2..n).inject(:*) end
def scount(a,b) a.each{|n|b[n]+=1} end
n = inp
a = inp
max = Array.new(1001){Array.new(2,0)}
0.upto(n-1) do |d|
  if(max[d][0] > 1)
    cop = [max[d][0],max[d][1]].max
    max[d+1][1] = [(max[d][0]+a[d]),max[d][1]].max
    max[d+1][0] = cop
  elsif(max[d][1] > 1)
    cop = [max[d][0],max[d][1]].max
    max[d+1][0] = [(max[d][0]+a[d]),max[d][1]].max
    max[d+1][0] = cop
  else
    max[d+1][1] = a[d]
  end
end
p max[n][1]