- 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
4 5 1 2 2 3 2 4 3 1 3 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.