n = int(input())
b = list(int(input()) for _ in range(n))
for i in range(1,n,2):
    if b[i-1] < b[i]:
        print(-1)
        exit()
a = [1]
for i in range(n):
    if i % 2 == 0:
        a.append(b[i] - a[-1])
    else:
        a.append(a[-1] - b[i])
print(n+1)
for i in range(n+1):
    print(a[i])