There are $n$ cities and $m$ flight connections. Your task is to check if you can travel from any city to any other city using the available flights.
The first input line has two integers $n$ and $m$ : the number of cities and flights. The cities are numbered $1,2,\dots,n$ .
After this, there are $m$ lines describing the flights. Each line has two integers $a$ and $b$ : there is a flight from city $a$ to city $b$ . All flights are one-way flights.
Print "YES" if all routes are possible, and "NO" otherwise. In the latter case also print two cities $a$ and $b$ such that you cannot travel from city $a$ to city $b$ . If there are several possible solutions, you can print any of them.
4 5 1 2 2 3 3 1 1 4 3 4· \n · \n · \n · \n · \n · \n
NO 4 2\n · \n