# Beer Bottles

You are given an integer `n`

representing `n`

full beer bottles. Given that you can exchange `3`

empty beer bottles for `1`

full beer bottle, return the number of beer bottles you can drink.

**Constraints**

`0 ≤ n < 2 ** 31`

https://binarysearch.com/problems/Beer-Bottles

## Examples

### Example 1

**Input**

- n =
`9`

**Output**

- answer =
`13`

**Explanation**

- In first round, we drink
`9`

beer bottles. - We can exchange the
`9`

empty ones for`3`

beer bottles. - We can exchange the
`3`

empty ones for`1`

beer bottle.

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