I start to feed one of the pigeons.
A minute later two more fly by and a minute after that another 3.
Then 4, and so on (Ex: 1+2+3+4+...). One portion of food lasts a pigeon for a minute,
but in case there's not enough food for all the birds, the pigeons who arrived first ate first.
Pigeons are hungry animals and eat without knowing when to stop.
If I have **N** portions of bird feed, how many pigeons will be fed with at least one portion of wheat?

**Input: ** A quantity of portions wheat as a positive integer.

**Output: ** The number of fed pigeons as an integer.

**Example:**

checkio(1) == 1 checkio(2) == 1 checkio(5) == 3 checkio(10) == 6

**How it is used: **
This task illustrates how we can model various situations.
Of course, the model has a limited approximation, but often-times we don't need a perfect model.

**Precondition: ** 0 < N < 10^{5}.