$11\mathrm{.}10$ 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$()$ function, which takes in an index $($starting at $0),n,$ 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.

the code:

#include

using namespace std;

int Fibonacci$($int n$)\{$

$/*$ Type your code here. $*/$

$\}$

int main$()\{$

int startNum;

cin $>>$ startNum;

cout $$ "Fibonacci$("$ startNum is $"$ Fibonacci$($startNum$)$ endl;

return $0$;

$\}$