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class Solution {
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 public:
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  pair<int, int> divmod(int dividend, int divisor) {
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    int quotient = dividend / divisor;
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    int remainder = dividend % divisor;
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    return make_pair(quotient, remainder);
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  }
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  int numWaterBottles(int numBottles, int numExchange) {
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    int result = numBottles;
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    pair<int, int> div = divmod(numBottles, numExchange);
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    int drunk = div.first;
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    int empty = div.second;
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    while (drunk) {
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      result += drunk;
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      div = divmod(drunk + empty, numExchange);
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      drunk = div.first;
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      empty = div.second;
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    }
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    return result;
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  }
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};