class xor_base():
    def __init__(self):
        self.K = 60
        self._list = [0] * self.K
        self.cnt = 0
        
    def min_all(self, x):
        for i in range(self.K - 1, -1, -1):
            if (x >> i) & 1:
                x ^= self._list[i]
        return x
    
    def add(self, x):
        x = self.min_all(x)
        if x == 0:
            return 0
        for i in range(self.K - 1, -1, -1):
            if (x >> i) & 1:
                for j in range(self.K):
                    if (self._list[j] >> i) & 1:
                        self._list[j] ^= x
                self._list[i] = x
                self.cnt += 1
                return 1
        return 0
            
    def get(self, x):
        now = 0
        for i in range(self.K):
            if self._list[i] == 0:
                continue
            if x & 1:
                now ^= self._list[i]
            x >>= 1
        return now
    
    def __len__(self):
        return self.cnt              
        
    def __str__(self):
        return f"{self._list}, len = {self.cnt}"
    
    
N = int(input())
A = list(map(int, input().split()))
X = xor_base()
XX = []
XX.append(X)
from copy import *
now = -1
ans = []
for i, a in enumerate(A):
    if a == 0:
        print(1)
        print(i + 1)
        exit()
    if not X.add(a):
        now = a
        ans.append(i+1) 
        break
    else:
        XX.append(deepcopy(X))
else:
    print(-1)
    exit()
        
ind = ans[-1] - 1
for i in range(ind, 0, -1):
    if not XX[i - 1].add(now ^ A[i - 1]):
        ans.append(i)
        now ^= A[i - 1]
        if now == 0:
            break
        
ans.sort()
if now == 0:
    print(len(ans))
    print(*ans)
else:
    print(-1)