## fibonacci2

### Instructions

Complete the body of the function `fibonacci`.

This functions receives a number n and returns the nth number in the fibonacci series.

The Fibonacci Series starts like this: 0, 1, 1, 2, 3, 5, 8, 13... so fibonacci(2) = 1 and fibonnacci(4) = 3


### Expected function

```rust
 fn fibonacci(n: u32) -> u32 {

 }
```

### Usage

Here is a possible test for your function:

```
#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn it_works() {
        assert_eq!(fibonacci(2), 1);
        assert_eq!(fibonacci(4), 1);
        assert_eq!(fibonacci(22), 17711);
        assert_eq!(fibonacci(20), 6765);
    }
}
```