- Time limit: 1.00 s
- Memory limit: 512 MB
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 $b$.
- $1 \le n \le 10^5$
- $1 \le m \le 2 \cdot 10^5$
- $1 \le a,b \le n$