n = gets.to_i

data = Array.new(n)
result = Array.new(n+1)

n.times{|i| data[i] = gets.to_i}

b = 1
result[0] = data[0]-1
    if (data[0]<=0)
        puts "-1";exit
    end
n.times{|i|
    b = result[i+1] = (data[i]-b) if i%2==0
    b = result[i+1] = (b-data[i]) if i%2==1
    
    if (b<=0 || 10**18<b)
        puts "-1";exit
    end
}

puts n+1
result.each{|e| puts e}

#0.upto(n-1){|i|
#    p result[i]+result[i+1] == data[i] if i%2==0
#    p result[i]-result[i+1] == data[i] if i%2==1
#}