# Problem Definition

## Description

You are a product manager and currently leading a team to develop a new product. Unfortunately, the latest version of your product fails the quality check. Since each version is developed based on the previous version, all the versions after a bad version are also bad.

Suppose you have `n` versions `[1, 2, ..., n]` and you want to find out the first bad one, which causes all the following ones to be bad.

You are given an API `bool isBadVersion(version)` which will return whether `version` is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API.

**Example:**

```plaintext
Given n = 5, and version = 4 is the first bad version.

call isBadVersion(3) -> false
call isBadVersion(5) -> true
call isBadVersion(4) -> true

Then 4 is the first bad version.
```

## Notes

1. [LeetCode discussion - O(lgN) simple Java solution](https://leetcode.com/explore/interview/card/top-interview-questions-easy/96/sorting-and-searching/774/discuss/71296/O(lgN)-simple-Java-solution)