# 0651. 4 Keys Keyboard

https://leetcode.com/problems/4-keys-keyboard

## Description

Imagine you have a special keyboard with the following keys:

* A: Print one `'A'` on the screen.
* Ctrl-A: Select the whole screen.
* Ctrl-C: Copy selection to buffer.
* Ctrl-V: Print buffer on screen appending it after what has already been printed.

Given an integer n, return _the maximum number of_ `'A'` _you can print on the screen with **at most**_ `n` _presses on the keys_.

**Example 1:**

```
**Input:** n = 3
**Output:** 3
**Explanation:** We can at most get 3 A's on screen by pressing the following key sequence:
A, A, A
```

**Example 2:**

```
**Input:** n = 7
**Output:** 9
**Explanation:** We can at most get 9 A's on screen by pressing following key sequence:
A, A, A, Ctrl A, Ctrl C, Ctrl V, Ctrl V
```

**Constraints:**

* `1 <= n <= 50`

## ac

```java
```
