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.

Solution