441. Arranging Coins

class Solution:
    def arrangeCoins(self, n):
        """
        :type n: int
        :rtype: int
        """
        i=1
        new_number = n
        while new_number >= 0:
            new_number = new_number-i
            i += 1
        return i-2


optimized version:
import math
class Solution:
    def arrangeCoins(self, n):
        """
        :type n: int
        :rtype: int
        """
        return int(math.sqrt(2 * n + 0.25) - 0.5)