I am trying to find the last digit of sum of Fibonacci Series. I calculate the sum as F(n+2) - 1. The below code is working fine but it is slow for large numbers (e.g 99999). How can I optimize this?

n = int(input())def last_digit(n):a, b = 0, 1for i in range(n+2):a, b = b, a + breturn (a-1) % 10print(last_digit(n))

Look at this table: http://www.maths.surrey.ac.uk/hosted-sites/R.Knott/Fibonacci/fibtable.html notice that fib(60) last digit is 0 and fib(61) last digit is 1, that is same as fib(0) and fib(1), thus starting at 60 last digits starts to repeat, so you can calculate last digit for fib(n%60) rather than fib(n). For example last digit is same for fib(115) and fib(55) and equal to 5.