HackerRank / Strange Counter / Python

https://www.hackerrank.com/challenges/strange-code/problem?isFullScreen=true

def strangeCounter(t):
    # Write your code here
    n_start = 3
    n = 3
    n_last = 0 #전에 n값을 저장
    while t > n:
        n_last = n
        a = n*2
        n = a + n_start
    length = n - n_last
    return length - (t-n_last) +1