TL（简单）

TL

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

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 2a ≤ 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.

纯粹找水题练练python。。。

 def getVar():
     return tuple(map(int, input().split()))

 n, m = getVar()
 a = getVar()
 b = getVar()
 c = max(min(a) * 2, max(a))
 d = min(b) - 1
 if c > d:
     c = -1
 print(c)