CF350A.TL

Valera wanted to prepare a Codesecrof round. He's already got one problem and he wants to set a time limit (TL) on it.

Valera has written n correct solutions. For each correct solution, he knows its running time (in seconds). Valera has also wrote m wrong solutions and for each wrong solution he knows its running time (in seconds).

Let's suppose that Valera will set v seconds TL in the problem. Then we can say that a solution passes the system testing if its running time is at most v seconds. We can also say that a solution passes the system testing with some "extra" time if for its running time, a seconds, an inequality 2_a_ ≤ v holds.

As a result, Valera decided to set v seconds TL, that the following conditions are met:

1. v is a positive integer;
2. all correct solutions pass the system testing;
3. at least one correct solution passes the system testing with some "extra" time;
4. all wrong solutions do not pass the system testing;
5. value v is minimum among all TLs, for which points 1, 2, 3, 4 hold.

Help Valera and find the most suitable TL or else state that such TL doesn't exist.

瓦莱拉想为 CodeSecrof 比赛准备一道题目。他目前已有一道题，并希望为其设定一个时间限制（Time Limit，简称 TL）。

瓦莱拉编写了 $n$ 个正确解法。对于每个正确解法，他已知其运行时间（单位：秒）。他还编写了 $m$ 个错误解法，并对每个错误解法也已知其运行时间（单位：秒）。

假设瓦莱拉将该题的 TL 设为 $v$ 秒。那么我们称一个解法通过系统测试，当且仅当它的运行时间不超过 $v$ 秒。进一步地，若某个解法的运行时间为 $a$ 秒，且满足不等式 $2a \le v$，则称该解法以一定的“余量”通过系统测试。

最终，瓦莱拉决定选择一个整数 $v$ 作为 TL，使得以下条件全部满足：

1. $v$ 是一个正整数；
2. 所有正确解法均能通过系统测试；
3. 至少有一个正确解法能以一定的“余量”通过系统测试；
4. 所有错误解法均不能通过系统测试；
5. 在所有满足条件 1–4 的 $v$ 中，$v$ 取最小值。

请帮助瓦莱拉找出最合适的 TL；若不存在满足条件的 TL，请说明其不存在。

The first line contains two integers n, m (1 ≤ n, m ≤ 100). The second line contains n space-separated positive integers _a_1, _a_2, ..., a__n (1 ≤ a__i ≤ 100) — the running time of each of the n correct solutions in seconds. The third line contains m space-separated positive integers _b_1, _b_2, ..., b__m (1 ≤ b__i ≤ 100) — the running time of each of m wrong solutions in seconds.

第一行包含两个整数 $n$、$m$（$1 ≤ n, m ≤ 100$）。
第二行包含 $n$ 个用空格分隔的正整数 $a_1, a_2, ..., a_n$（$1 ≤ a_i ≤ 100$）——表示 $n$ 个正确解法各自的运行时间（单位：秒）。
第三行包含 $m$ 个用空格分隔的正整数 $b_1, b_2, ..., b_m$（$1 ≤ b_i ≤ 100$）——表示 $m$ 个错误解法各自的运行时间（单位：秒）。

If there is a valid TL value, print it. Otherwise, print -1.

如果存在有效的 TL 值，则输出该值；否则输出 -1。