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.
4 5 1 2 2 3 2 4 3 1 3 4· \n · \n · \n · \n · \n · \n
4\n
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 $3 \rightarrow 1 \rightarrow 2 \rightarrow 4$ .