Negafibonacci numbers?

Number Theory Level 2

The Fibonacci numbers are given by

$F(0) = 0$
$F(1) = 1$
$F(n) = F(n-1) + F(n-2).$

So, the first few are $0, 1, 1, 2, 3, 5, 8, 13.$

If we generalize this to negative numbers, what is $F(-8)?$