n=gets.to_i
b=[]
n.times do
  b<< gets.to_i
end

l, r=1, 10**18
b.each_with_index do |e, i|
  if i.even?
    if e<=l
      puts (-1)
      exit(0)
    end
    l, r=[1, e-r].max, e-l
  else
    if r<=e
      puts (-1)
      exit(0)
    end
    l, r=[1, l-e].max, r-e
  end
end

if l>r
  puts (-1)
  exit(0)
end

a=[(l+r)/2]
(n-1).downto 0 do |i|
  if (i+1).even?
    a<< b[i]+a.last
  else
    a<< b[i]-a.last
  end
end

puts a.size
a.reverse.map{|e| puts e}