public static void Test()
{
Solution s = new Solution();
int bt = 9, ex = 3;
Console.WriteLine($"{bt} {ex} " + s.NumWaterBottles(bt, ex));
bt = 15;
ex = 4;
Console.WriteLine($"{bt} {ex} " + s.NumWaterBottles(bt, ex));
bt = 5;
ex = 5;
Console.WriteLine($"{bt} {ex} " + s.NumWaterBottles(bt, ex));
bt = 2;
ex = 3;
Console.WriteLine($"{bt} {ex} " + s.NumWaterBottles(bt, ex));
}