Imagine you have a special keyboard with the following keys: 

Key 1:  Prints 'A' on screen
Key 2: (Ctrl-A): Select 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.

Find maximum numbers of A's that can be produced by pressing keys on the special keyboard N times. 

Example 1:

Input: N = 3
Output: 3
Explaination: Press key 1 three times.

Example 2:

Input: N = 7
Output: 9
Explaination: The best key sequence is 
key 1, key 1, key 1, key 2, key 3,
key4, key 4.

Your Task:
You do not need to read input or print anything. Your task is to complete the function optimalKeys() which takes N as input parameter and returns the maximum number of A's that can be on the screen after performing N operations.

Expected Time Complexity: O(N²)
Expected Auxiliary Space: O(N)

Constraints:
1 < N < 75