import random
from time import time

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

st = time()

def solve(check: list[int]):
    K = len(check)
    # B[i] をcheckの桁だけ取り出したもの
    B = [0]*N
    for i in range(N):
        for j in range(K):
            B[i] ^= (A[i]>>check[j]&1)<<j
    
    # dp[i][j][k] := i桁目まで見て、jが作れるか？kは1個以上使ったかどうか
    dp = [[[False, False] for _ in range(1<<K)] for _ in range(N+1)]
    dp[0][0][0] = 1
    for i in range(N):
        for j in range(1<<K):
            for k in range(2):
                dp[i+1][j^B[i]][1] |= dp[i][j][k]
                dp[i+1][j][k] |= dp[i][j][k]
    
    if not dp[N][0][1]:
        return
    
    # 復元
    ans = []
    j = 0
    k = 1
    for i in range(N-1, -1, -1):
        # dp[i+1][j][k] が True であることが保証
        for nk in range(2):
            if dp[i][j^B[i]][nk]:
                j ^= B[i]
                k = nk
                ans.append(i+1)
                break
    
    T = 0
    for i in ans:
        T ^= A[i-1]
    if T == 0:
        print(len(ans))
        print(*ans)
        exit()

while time()-st < 1.9:
    check = random.sample(range(60), 5)
    solve(check)

print(-1)