Dominoes#1104
Dominoes can inspire a variety of entertaining activities. For example, children enjoy arranging dominoes in a line, placing them side by side. If you push one tile, it falls and knocks down the next one, which in turn knocks down the following one, and so on, until the chain reaction stops. However, there may be arrangements where not all tiles fall. In such cases, you need to push another tile to keep the chain reaction going.
The first line contains two integers and (1 \le n, m \le 10^5), where is the number of domino tiles, and is the number of lines describing their interactions. The dominoes are numbered from to .
Each of the following lines contains two integers and , indicating that if the domino numbered falls, it will knock over the domino numbered .
Print one integer — the minimum number of dominoes that need to be pushed to make all the dominoes fall.
Example 1
Example 2