Dwarves go to the stream to fetch water. Each dwarf's bucket has a different volume: 3, 4, 5, 6, 7, 8, and 9 liters. The dwarves do not lend their buckets to each other and always bring them back full of water.

- Kejchal brings more water in his bucket than Štístko.
- Dřímal would have to go for water three times to bring exactly as much water as Stydlín in one of his buckets.
- Próf's bucket is only 2 liters larger than Štístko's.
- Šmudla himself brings as much water as Dřímal and Štístko together.
- When Prófa and Šmudla go for water, they bring the same amount of water as Rejpal, Kejchal, and Štístko.

How much water will Kejchal and Šmudla bring together?

(M. Petrová)

Idea. Start with the second condition.
From the second condition, it follows that Drímal's jug has a volume of 3 liters and Stydlín's 9 liters (since $3 \cdot 3=9$, and if Drímal's jug were different, Stydlín's jug would have to be at least a twelve-liter one).

Now, from the fourth condition, it follows that Šmudl's jug is 3 liters larger than Štístko's. Together with the third condition, we know that Štístko, Prófa, and Šmudl have jugs with volumes of either 4, 6, and 7 liters, or 5, 7, and 8 liters, respectively.

From the first condition, it then follows that the only possible ways the dwarves could have distributed the jugs are:

| 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| :---: | :---: | :---: | :---: | :---: | :---: | :---: |
| Drímal | Štístko | Kejchal | Prófa | Šmudl | Rejpal | Stydlín |
| Drímal | Štístko | Rejpal | Prófa | Šmudl | Kejchal | Stydlín |
| Drímal | Rejpal | Štístko | Kejchal | Prófa | Smudl | Stydlín |

If we verify the last, fifth, condition, we find that the first two marked options do not work $(6+7 \neq 8+5+4)$, while the third one does $(7+8=4+5+6)$. Therefore, Kejchal and Šmudl together will bring $6+8=14$ liters of water.