n = int(input())
a = list(map(int, input().split()))

assert 1 <= n <= 2 * 10**5
assert len(a) == n
assert all(0 <= x <= 1 << 60 for x in a)

if n > 61:
    n = 61
    a = a[:61]

idx_list = [{i} for i, _ in enumerate(a)]

pivot = 0
for i in range(60):
    for j in range(pivot, n):
        if a[j] & (1 << i):
            a[pivot], a[j] = a[j], a[pivot]
            idx_list[pivot], idx_list[j] = idx_list[j], idx_list[pivot]
            break
    else:
        continue
    
    for j in range(n):
        if j == pivot:
            continue
        if a[j] & (1 << i):
            a[j] ^= a[pivot]
            idx_list[j] |= idx_list[pivot]
    
    pivot += 1

if 0 in a:
    zero_idx = a.index(0)
    b = [i + 1 for i in idx_list[zero_idx]]
    print(len(b))
    print(*b)
else:
    print(-1)