D = int(input())
A = list(map(int, input().split()))
c = A[0]
x, y = -c, -c
for i, v in enumerate(A):
    x += v
    y += v * (-1) ** (i%2)
a = (x + y)//2
b = (x - y)//2
if a == 0:
    if b == 0:
        print(0)
        print(c)
    else:
        print(1)
        print(c, b)
else:
    print(2)
    print(c, b, a)