D = int(input())
As = list(map(int, input().split()))
a = As[0]
b = sum(As)
c = sum(As[::2])
r0 = a
r1 = b - c
r2 = c - a
if r2 != 0:
    print(2)
    print(r0, r1, r2)
elif r1 != 0:
    print(1)
    print(r0, r1)
else:
    print(0)
    print(r0)