N = input()
b = [int(raw_input()) for _ in xrange(N)]
a = [0 for _ in xrange(N+1)]
a[0] = 1
for i in xrange(1, N+1):
    a[i] = b[i-1] - a[i-1] if i % 2 == 1 else a[i-1] - b[i-1]
    if a[i] <= 0:
        print -1
        exit()
print N+1
for x in a:
    print x