Look at the constraints! Your "solution" doesn't even work for any a,b > 1473.
[bbone=Python,82]>>> 1.61803398875**1475
Traceback (most recent call last):
File "", line 1, in
OverflowError: (34, 'Numerical result out of range')[/bbone]
As hendrik said: You need another approach. And: Try to write "readable Python", not "short Python".