import sys, threading

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

basis, comb = [0]*60, [None]*60

for idx, Ai in enumerate(A_list):
    v, cmb = Ai, {idx: 1}
    for k in reversed(range(60)):
        if (v >> k) & 1:
            if not basis[k]:
                basis[k], comb[k] = v, cmb.copy()
                break
            v ^= basis[k]
            for key, val in comb[k].items():
                cmb[key] = (cmb.get(key, 0) + val) % 2
    else:
        ans = sorted(i+1 for i, cnt in cmb.items() if cnt % 2)
        print(len(ans))
        print(' '.join(map(str, ans)))
        exit()

print(-1)

threading.Thread(target=lambda: None).start()