|Codeforces Round #546 (Div. 2)|
Finished her homework, Nastya decided to play computer games. Passing levels one by one, Nastya eventually faced a problem. Her mission is to leave a room, where a lot of monsters live, as quickly as possible.
There are $$$n$$$ manholes in the room which are situated on one line, but, unfortunately, all the manholes are closed, and there is one stone on every manhole. There is exactly one coin under every manhole, and to win the game Nastya should pick all the coins. Initially Nastya stands near the $$$k$$$-th manhole from the left. She is thinking what to do.
In one turn, Nastya can do one of the following:
Nastya can leave the room when she picks all the coins. Monsters are everywhere, so you need to compute the minimum number of moves Nastya has to make to pick all the coins.
Note one time more that Nastya can open a manhole only when there are no stones onto it.
The first and only line contains two integers $$$n$$$ and $$$k$$$, separated by space ($$$2 \leq n \leq 5000$$$, $$$1 \leq k \leq n$$$) — the number of manholes and the index of manhole from the left, near which Nastya stays initially. Initially there is exactly one stone near each of the $$$n$$$ manholes.
Print a single integer — minimum number of moves which lead Nastya to pick all the coins.
Let's consider the example where $$$n = 2$$$, $$$k = 2$$$. Nastya should play as follows:
So, $$$6$$$ moves are required to win.