#### Find the Missing Number

You are given an unsorted array of integers as an argument. When sorted, the numbers in the array will form a sequence. One number in the sequence is missing. Return the missing number.

### Requirements

- Must return a single integer.
- Number returned must be between the 0th and Kth index of the given array when sorted.
- Must also work with negative integers

#### Example 1

```
solve([5, 0, 2, 1, 3])
> 4
```

*Sorted, the array will be 0,1,2,3,5, The missing number in this sequence is 4*

#### Example 2

```
solve([-5, 0, -2, -1, -3])
> 4
```

*Sorted, the array will be -5, -3, -2, -1, 0, The missing number in this sequence is -4*