from collections import deque

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

while len(A) > 61:
    A.pop()
    N -= 1

B = [[0]*60 for _ in range(N)]
for i in range(N):
    for j in range(60):
        if 1<<j & A[i]:
            B[i][59-j] = 1

row = 0
idx = list(range(N))
ans = []
G = [[] for _ in range(N)]
for j in range(60):
    pivot = row
    while pivot < N and B[pivot][j] == 0:
        pivot += 1
    if pivot == N:
        continue
    B[row], B[pivot] = B[pivot], B[row]
    idx[row], idx[pivot] = idx[pivot], idx[row]
    for i in range(row+1, N):
        if i != row and B[i][j] == 1:
            G[i].append(row)
            for k in range(60):
                B[i][k] ^= B[row][k]
    row += 1

if max(B[-1]) == 0:
    que = deque()
    que.append(i)
    ans = set([idx[-1]+1])
    while que:
        n = que.popleft()
        for v in G[n]:
            if idx[v]+1 in ans:
                ans.remove(idx[v]+1)
            else:
                ans.add(idx[v]+1)
            que.append(v)
    print(len(ans))
    print(*ans)
else:
    print(-1)