import math

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

fixed = []
for a in A:
    if a != -1:
        fixed.append(a)

if not fixed:
    print(-1)
else:
    g = fixed[0]
    for num in fixed[1:]:
        g = math.gcd(g, num)
    print(g * g)