**English**RU

You have a Domino box. Domino tiles contain two numbers from 0 (empty) to 6. Tiles are unordered and 1-6 is the same as 6-1. The double-six set contains 28 unique tiles - all combinations of number pairs.

Several tiles fell out of the box. You should try to line up a chain from these tiles, compiling them to each other's suitable sides (sides with the same numbers). Thus, you can get a continuous chain of tiles. In some cases, such a chain will not be the only one.

For example, you've ended up these tiles:

**1-5, 2-5, 3-5, 4-5, 3-4**

So, with them you can build two complete chains:

**1-5, 5-3, 3-4, 4-5, 5-2**

**1-5, 5-4, 4-3, 3-5, 5-2**

**Your goal in this mission** is to count how many complete chains you can make using all of the given dominoes.

**Note.** Chains must be unique. An inverted chain is not considered as unique: "1-2, 2-3, 3-4, 4-5" and "5-4, 4-3, 3-2, 2-1" are the same chain.

**Input:**
String with the description of the domino tiles. Like this one: "5-4, 4-3, 3-2, 2-1".

**Output:**
Integer. The maximum number of complete chains that you can build using all of the given tiles.

**Examples:**

domino_chain("0-2, 0-5, 1-5, 1-3, 5-5") == 1 domino_chain("1-5, 2-5, 3-5, 4-5, 3-4") == 2 domino_chain("0-5, 1-5, 2-5, 3-5, 4-5, 3-4") == 0

**How it is used:**
This is a combinatorial problem. You can solve it by modeling a real game of dominoes. Or refreshing your knowledge of graph theory. Many things in life resemble the process of forming a domino chain: for example, flights between several cities.

**Precondition:**
5 <= len(given_tiles) <= 17