def main():
    _ = int(input())
    a = set(list(map(int, input().split())))

    ans = -1
    for d in range(12):
        lst = set(map(lambda x: x % 12, [d, d + 2, d + 4, d + 5, d + 7, d + 9, d + 11]))
        if a <= lst:  # 部分集合
            if ans == -1:
                ans = d
            else:
                exit(print(-1))
    print(ans)


if __name__ == "__main__":
    main()