import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
######################################################################

def popcount(x):
    r = 0
    while x:
        r += x & 1
        x >>= 1
    return r

n = ni()
a = na()

base = []

for i in range(n):
    x = a[i]
    f = 1 << i
    for b in base:
        if x ^ b[0] < x:
            x ^= b[0]
            f ^= b[1]
    if x:
        base.append((x, f))
    else:
        print(popcount(f))
        print(*[i + 1 for i in range(n) if f & (1 << i)])
        break
else:
    print(-1)