n = int(input())
A = list(map(int, input().split()))
B = []
bits = []

for i, a in enumerate(A):
    x = 1 << i
    for b, bit in zip(B, bits):
        if b ^ a < a:
            a ^= b
            x ^= bit

    if a == 0:
        lst = [i + 1 for i in range(100) if x >> i & 1]
        print(len(lst))
        print(*lst)
        exit()

    B.append(a)
    bits.append(x)

print(-1)