n=gets.to_i
a=[]
n.times do |i|
  a<< gets.to_i
end
c=1
e=0
while true do
b=[]
b<< 2-c
(n/2).times do |i|
  b<< a[i*2]-b[i*2]
  b<< b[i*2+1]-a[i*2+1]
end
(n%2).times do
  b<< a[-1]-b[-1]
end
if b.all?{|i|i>0}
  puts n+1,b.*("\n")
  break
elsif e==1
  p -1
  break
end
c=1
(n+1).times do |i|
  c=b[i] if c>b[i]
end
e+=1
end