d = int(input())
A = list(map(int, input().split()))
x = 0
y = 0
for i, a in enumerate(A):
    if i%2 == 0:
        x += a
        y += a
    else:
        x += a
        y -= a
b0 = A[0]
b1 = (x-y)//2
b2 = (x+y-2*b0)//2
if b2 == 0:
    if b1 == 0:
        print(0)
        print(b0)
    else:
        print(1)
        print(b0, b1)
else:
    print(2)
    print(b0, b1, b2)