D = int(input())

A = list(map(int, input().split()))

a = A[0]

b = sum(A[1::2] + [0])

c = sum(A[2::2] + [0])

if c != 0:
    print(2)
    print(a, b, c)
    
elif b != 0:
    print(1)
    print(a, b)
else:
    print(0)
    print(a)