n = int(input())
b = [int(input()) for i in range(n)]

if b[0] == 1:
    print(-1)

a = [1]
for i in range(n):
    if i%2 == 0:
        a.append(b[i] - a[i])
    elif i%2 == 1:
        a.append(a[i] - b[i])
    if a[-1] <= 0:
        print(-1)
        exit()

print(n+1)
for v in a:
    print(v)