Library

After the crisis caused by the appearance of artificial intelligence for programming, you decided to get a job at a library. You were made responsible for $n$ books, each of which has its own name, but for convenience, you decided to number them from $1$ to $n$. Each book is kept in the library in a single copy. Initially, all books are available in the library. On the first day, $m$ people visited you, each of whom wanted to return or receive a book. Find the number of people who failed to get the desired book.

Input

The first line contains two integers $n$ and $m$ ($1\le n\le 1000$, $1\le m\le 5000$) — the number of books and visitors, respectively.

The next $m$ lines contain two integers $t$ and $x$ ($1\le t\le 2,1\le x\le n$), which describe the corresponding visitor. If $t=1$, the visitor is trying to get the book with number $x$, If $t=2$, the visitor wants to return the book with number $x$.

It is guaranteed that if a book is returned to the store, then it was taken from it.

Output

Output a single integer — the answer to the problem.

Examples

Note

In the first example, there are $2$ books in the library. Both books are available in the store for the first visitor.

The first visitor comes and tries to take the book with number $2$, since it is in the library, he takes it and leaves.

Then the second visitor comes and takes the book with number $1$, since it is in the library.

The third visitor wants to take the book with number $1$, but he cannot do this because it has already been taken by the second visitor.

Then the second visitor comes and returns the book with the number $1$.

The fifth visitor wants to take the book with number $2$, but it has already been taken by the first visitor, so he takes nothing and goes home.

The sixth visitor wants to take the book with number $1$, since it is available, he takes it and goes home.

A total of two people failed to get the desired book, so the answer is $2$.