Lucas numbers are numbers in a sequence defined like this:
L(0) = 2
L(1) = 1
L(n) = L(n-1) + L(n-2)
Your mission is to complete the function that returns the nth term of this sequence.
Note: It should work for negative numbers as well; how you do this is you flip the equation around, so for negative numbers: L(n) = L(n+2) - L(n+1)
L(-10) = 123
L(-5) = -11
L(-1) = -1
L(0) = 2
L(1) = 1
L(5) = 11
L(10) = 123