def main():
    import sys
    from fractions import gcd
    input = sys.stdin.readline

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

    if sum(A) == -N:
        print(-1)
        exit()

    g = 0
    for a in A:
        if a != -1:
            g = gcd(g, a)
    print(g**2)


if __name__ == '__main__':
    main()