Thank you for your time.i really apreciate your efford! I tweaked it a bit to make it fully functional
def fib(n):
if n == 0:
return 0
a, b = 0, 1
for i in range(n-1):
a, b = b, a + b
return b
user_input=input()
while user_input!="END":
user_input=int(user_input)
print (fib(user_input))
user_input=input()
