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class Solution {
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  public int numWaterBottles(int numBottles, int numExchange) {
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    int drinkedBottles = numBottles;
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    int emptyBottles = numBottles;
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    while (emptyBottles >= numExchange) {
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      int gainedBottles = emptyBottles / numExchange;
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      drinkedBottles += gainedBottles;
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      int unusedEmptyBottles = emptyBottles % numExchange;
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      emptyBottles = gainedBottles + unusedEmptyBottles;
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    }
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    return drinkedBottles;
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  }
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}