PROGRAMMING:Match pilot
The flight brigade has several pilots from all over the world, who are specialized in flying one type of aircraft. Each aircraft has two pilots, one pilot and one co pilot. Due to various reasons, such as the problem of mutual cooperation, some pilots can't fly on the same aircraft. How to match the pilots to make the most flights.
Because of the strict division of work, two pilots or two co pilots can not fly on the same plane.
###Input format:
In the first line, two integers, $$n $$and $$M $$, indicate that there are a total of $$n $$pilots, of which $$M $$pilots are pilots.
There are several lines below, each with $$2 $$numbers $$a, B $$. Indicates that the pilot $$a $$and co pilot $$B $$can fly in the same plane.
Note: the number of the chief driver comes first, that is, the number of the chief driver is less than that of the co driver.
The data is guaranteed to be $$2 / Leq n / Leq 100$$
###Output format:
There is only one integer in one line, which represents the maximum number of planes to take off.
###Input example:
Here is a set of inputs. For example:
```in
10 5
1 7
2 6
2 10
3 7
4 8
5 9
```
###Output example:
The corresponding output is given here. For example:
```out
four
```
answer：If there is no answer, please comment
Because of the strict division of work, two pilots or two co pilots can not fly on the same plane.
###Input format:
In the first line, two integers, $$n $$and $$M $$, indicate that there are a total of $$n $$pilots, of which $$M $$pilots are pilots.
There are several lines below, each with $$2 $$numbers $$a, B $$. Indicates that the pilot $$a $$and co pilot $$B $$can fly in the same plane.
Note: the number of the chief driver comes first, that is, the number of the chief driver is less than that of the co driver.
The data is guaranteed to be $$2 / Leq n / Leq 100$$
###Output format:
There is only one integer in one line, which represents the maximum number of planes to take off.
###Input example:
Here is a set of inputs. For example:
```in
10 5
1 7
2 6
2 10
3 7
4 8
5 9
```
###Output example:
The corresponding output is given here. For example:
```out
four
```
answer：If there is no answer, please comment