There are $n$ cities and $m$ flight connections between them. A city is called a critical city if it appears on every route from a city to another city.
Your task is to find all critical cities from Syrjälä to Lehmälä.
The first input line has two integers $n$ and $m$ : the number of cities and flights. The cities are numbered $1,2,\dots,n$ . City $1$ is Syrjälä, and city $n$ is Lehmälä.
Then, there are $m$ lines describing the connections. Each line has two integers $a$ and $b$ : there is a flight from city $a$ to city $b$ . All flights are one-way.
You may assume that there is a route from Syrjälä to Lehmälä.
First print an integer $k$ : the number of critical cities. After this, print $k$ integers: the critical cities in increasing order.
5 5 1 2 2 3 2 4 3 5 4 5· \n · \n · \n · \n · \n · \n
3 1 2 5\n · · \n