$3\mathrm{.}15$ LAB: Fibonacci sequence $($recursion$)$

The Fibonacci sequence begins with $0$ and then $1$ follows. All subsequent values are the sum of the previous two, for example: $0,1,1,2,3,5,8,13.$ Complete the fibonacci$()$ method, which takes in an index, n$,$ and returns the nth value in the sequence. Any negative index values should return $-1.$

Ex: If the input is:

$7$

the output is:

fibonacci$(7)$ is $13$

Note: Use recursion and DO NOT use any loops.