def convolve_and(A, B):
    n = max(len(A), len(B))
    l = ((n - 1).bit_length())
    n = 1 << l
    A += [0] * (n - len(A))
    B += [0] * (n - len(B))
    
    def f(A):
        for i in range(l):
            for bit in range(n):
                if not bit >> i & 1:
                    A[bit] += A[bit ^ (1 << i)]
    
    def invf(A):
        for i in range(l):
            for bit in range(n):
                if not bit >> i & 1:
                    A[bit] -= A[bit ^ (1 << i)]
    
    f(A)
    f(B)
    C = [a * b for a, b in zip(A, B)]
    invf(C)
    return C

from math import gcd

n = int(input())
A = list(map(int, input().split()))
for i in range(n):
    if A[i] == -1:
        A[i] = 0
C = convolve_and(A[:], A[:])
g = 0
for c in C:
    g = gcd(c, g)
if g == 0:
    g = -1
print(g)