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

B = []
BIT = []
for i in range(N):
    bit = 1<<i
    a = A[i]
    for j in range(len(B)):
        if a^B[j] < a:
            a ^= B[j]
            bit ^= BIT[j]
    if a:
        B.append(a)
        BIT.append(bit)
    else:
        ans = []
        for j in range(i+1):
            if 1<<j & bit:
                ans.append(j+1)
        print(len(ans))
        print(*ans)
        break
else:
    print(-1)