# your code goes here
class Solution(object):
    def numWaterBottles(self, numBottles, numExchange):
        """
        :type numBottles: int
        :type numExchange: int
        :rtype: int
        """
        total = numBottles  # 9
        rest = total  # 9 
 
        while rest / numExchange > 0: # 9 / 3 = 3 
            total += (rest // numExchange) 
            rest = (rest % numExchange) + (rest // numExchange)
 
        return total 

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