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**Task** | Statistics

Time limit: | 1.00 s | Memory limit: | 512 MB |

There are $n$ cities with airports but no flight connections. You are given $m$ requests which routes should be possible to travel.

Your task is to determine the minimum number of one-way flight connections which makes it possible to fulfil all requests.

The first input line has two integers $n$ and $m$: the number of cities and requests. The cities are numbered $1,2,\dots,n$.

After this, there are $m$ lines describing the requests. Each line has two integers $a$ and $b$: there has to be a route from city $a$ to city $b$. Each request is unique.

Print one integer: the minimum number of flight connections.

- $1 \le n \le 10^5$

- $1 \le m \le 2 \cdot 10^5$

- $1 \le a, b \le n$

Input:

`4 5`

1 2

2 3

2 4

3 1

3 4

Output:

`4`

Explanation: You can create the connections $1 \rightarrow 2$, $2 \rightarrow 3$, $2 \rightarrow 4$ and $3 \rightarrow 1$. Then you can also fly from city $3$ to city $4$ using the route $3 \rightarrow 1 \rightarrow 2 \rightarrow 4$.