Some numbers can be expressed as a difference of two squares, for example, 20 = 6^(2)-4^(2) and 21 = 5^(2)-2^(2). Many numbers can be written this way, but not all.
## Your Task
Complete the function that takes a positive integer `n` and returns the amount of numbers between `1` and `n` (inclusive) that can be represented as the difference of two perfect squares.
**Note**: Your code should be able to handle `n` values up to 45000
## Examples
```
n = 4 ==> 3
n = 5 ==> 4
n = 10 ==> 7
n = 20 ==> 15
n = 6427 ==> 4820
```
count_squareable=lambda n:int(n*.75+0.25)
count_squareable=lambda n:int(n*.75+0.25)