651. 4 Keys Keyboard

Imagine you have a special keyboard with the following keys:

Key 1: (A) : Print one 'A' on screen.

Key 2: (Ctrl-A) : Select the whole screen.

Key 3: (Ctrl-C) : Copy selection to buffer.

Key 4: (Ctrl-V) : Print buffer on screen appending it after what has already been printed.

Now, you can only press the keyboard for N times (with the above four keys), find out the maximum numbers of 'A' you can print on screen.

Example 1:

Input:

 N = 3
Output:

 3
Explanation:

 
We can at most get 3 A's on screen by pressing 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

Note:

1. 1 <= N <= 50
2. Answers will be in the range of 32-bit signed integer.