'''
from random import randint
N = 60
A = set()
while len(A) < N:
    A.add(randint(1, (1<<(N-1))-1))
A = sorted(list(A))
'''
N = int(input())
A = list(map(int,input().split()))
N = min(61,N)

tmp = 0
for a in A:
    tmp |= a

A2 = []
for i in range(N):
    A2.append([A[i],[i]])
def f():
    tmp = 1
    for i in range(N - 1):
        f = True
        cmp = -1
        for j in range(N):
            if f:
                if A2[j][0] & tmp:
                    f = False
                    cmp = A2[j][0]
                    idx = A2[j][1]
            else:
                if A2[j][0] & cmp & tmp:
                    A2[j][0] ^= cmp
                    tmp2 = A2[j][1] + idx
                    tmp2.sort()
                    tmp3 = []
                    n = len(tmp2)
                    i = 0
                    while i < n:
                        if i < n - 1 and tmp2[i] == tmp2[i+1]:
                            i += 2
                        else:
                            tmp3.append(tmp2[i])
                            i += 1
                    A2[j][1] = tmp3

        tmp <<= 1
i = 0
while i < 20 and A2[0][0] > 0:
    f()
    A2.sort()
    i += 1
#print(A)
#print(A2[0])
#print("cnt", i)

tmp = 0
for i in A2[0][1]:
    tmp ^= A[i]
#print(tmp)
#print()

if A2[0][0] == 0:
    print(len(A2[0][1]))
    print(*[i + 1 for i in A2[0][1]])
else:
    print(-1)