def fiboTail(n):
	a, b = 0, 1
	while True:
	 if n > 1:
	 	n, a, b = n-1, b, a+b
	 elif n == 1:
	 	return b
	 elif n == 0:
	 	return a
	 else:
	 	raise IndexError
	 	
print("Result: %d" % fiboTail(80))