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