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

import copy
S=copy.deepcopy(A)

for i in range(N-1,-1,-1):
    for j in range(19):
        if i & (1<<j)!=0:
            if S[i]==-1:
                S[i^(1<<j)]=-1
            elif S[i]!=-1 and S[i^(1<<j)]!=-1:
                S[i^(1<<j)]+=S[i]

if max(S)==-1:
    print(-1)
else:    
    import math
    ANS=0
    for s in S:
        if s==-1:
            continue
        ANS=math.gcd(s**2,ANS)

    print(ANS)