N=int(input())
A=list(map(int,input().split()))
if N>=100:
    N=100
    A=A[:N]
B=[1<<i for i in range(N)]
tria=[]
for i in range(N):
    a=A[i]
    b=B[i]
    for x,y in tria:
        if a^x<a:
            a=a^x
            b=b^y
    if a==0:
        ans_lst=[i for i in range(N) if b&1<<i]
        print(len(ans_lst))
        print(*[ans+1 for ans in ans_lst])
        break
    else:
        prev=tria
        tria=[]
        for x,y in prev:
            if x^a<x:
                x=x^a
                y=y^b
            tria.append((x,y))
        tria.append((a,b))
else:
    print(-1)