base=[]
N=int(input())
base_dat=[[] for _ in range(N)]
A=list(map(int,input().split()))
for j in range(N):
    v=A[j]
    base_d=[]
    for i in range(len(base)):
        e=base[i]
        if v>v^e:
            base_d.append(i)
            v=v^e
    if v==0:
        dat=[0 for _ in range(N)]
        ans=[]
        dat[j]=1
        base_dat[j]=base_d[::]
        for k in range(j,-1,-1):
            if dat[k]%2==1:
                ans.append(k)
                for t in base_dat[k]:
                    dat[t]+=1
        #print(dat)
        #print(base_dat,base_d)
        print(len(ans))
        print(*[a+1 for a in sorted(ans)])
        exit(0)
    if v>0:
        base.append(v)
    base_dat[j]=base_d[::]
print(-1)