# Exercise: Fibonacci Series

Let's implement the Fibonacci series using loops!

## We'll cover the following

## Problem Statement

Fibonacci sequence is a series of numbers where every number is the sum of the two numbers before it. The first two numbers are `0`

and `1`

:

```
0 1 1 2 3 5 8 13
```

You must write the `fib()`

function which takes in a positive integer, `n`

, and returns the *n-th* Fibonacci number. However, instead of using recursion, your function must use any of the loops.

### Sample Input

```
n = 7
```

### Sample Output

```
8
```

## Coding Challenge

Take some time to figure out how the recursive approach can be translated into an iterative one. Consider all edge cases that could occur.

If `n`

is negative or zero, return `-1`

.

If you feel stuck, feel free to refer to the solution review in the next lesson.

Good luck!

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