a = 1
b = 1
 
n = input("input N:")
n = int(n) # преобразование в целое число
 
i = 2 
while i < n:
    result = b+ a
    a = b
    b = result
    i += 1
 
print (result)

>>> a, b, i = 1, 1, 2
>>> n = int(input("n"))
n6
>>> while i < n:
...    result = b + a
...    a, b = b, result
...    i += 1
... 
>>> print (result)
8

# -*- coding: utf-8 -*-
import sys
a, b, i = 1,1,2
n = int(sys.argv[1])
while i < n:
    result = b + a
    a, b = b, result
    i +=1
print(result)