def find_zero_xor_subset(nums):
    n = len(nums)
    max_bit = max(nums).bit_length()
    basis = [None] * max_bit  # 基底ベクトルを格納
    basis_indices = [None] * max_bit  # 基底ベクトルの元のインデックス
    index_combinations = [{} for _ in range(max_bit)]  # 基底ベクトルの組み合わせ

    for idx, num in enumerate(nums):
        coefficients = {}  # 現在の数の基底ベクトル表現
        coefficients[idx] = 1
        temp = num

        for i in reversed(range(max_bit)):
            if (temp >> i) & 1:
                if basis[i] is None:
                    basis[i] = temp
                    basis_indices[i] = idx
                    index_combinations[i] = coefficients
                    break
                else:
                    temp ^= basis[i]
                    coefficients = xor_dicts(coefficients, index_combinations[i])

        if temp == 0:
            # xorがゼロとなる部分集合を発見
            result_indices = sorted(coefficients.keys())
            return result_indices  # インデックスのリストを返す

    return None  # 存在しない場合


def xor_dicts(a, b):
    result = a.copy()
    for k in b:
        if k in result:
            del result[k]
        else:
            result[k] = b[k]
    return result


N = int(input())
A = list(map(int, input().split()))
ans = find_zero_xor_subset(A)
if ans == None:
    print(-1)
else:
    print(len(ans))
    ans = [x+1 for x in ans]
    print(*ans)