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

if b[0] == 1:
    print(-1)
    exit()
l = 1
r = b[0]-1
m = (l+r)//2
while l<r:
    ok = True
    a = [m]
    i = 0
    while i < 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:
            ok = False
            break
        i += 1
    if ok:
        print(n+1)
        for v in a:
            print(v)
        exit()
    if i%2 == 0:
        l = m+1
    else:
        r = m-1
    m = (l+r)//2
print(-1)