In the ACM kingdom, there are $N$ cities connected by $M$ two-way roads. These cities are connected, i.e., one can reach from any city $X$ to any other city $Y$ by going through some of these roads. One day, the government wishes to assign for each road a direction, such that one can still reach from any city to any other. You are asked to determine whether this task is possible.

-----Input-----
The first line of each test case consists of two integers, $N$ ($1 \leq N \leq 50$), and $M$ ($1 \leq M \leq N(N - 1)/2$). Each of the next $M$ lines describes a road, and consists of two integers, $X$ and $Y$, ($1 \leq X, Y \leq N$; $X \neq Y$), indicating that there is a road between city $X$ and $Y$. There is at most one road that directly connects each pair of cities.

-----Output-----
If it is impossible, output a single line NO. Otherwise, output YES on the first line, followed by $M$ lines describing one possible direction assignment to these $M$ roads. Each of these $M$ lines should consist of two integers, $X$, $Y$, indicating that there is a one-way road from city $X$ to city $Y$. These $M$ lines can be output in any order.

-----Examples-----
Sample Input 1:
3 3
1 2
2 3
1 3
Sample Output 1:
YES
1 3
2 1
3 2

Sample Input 2:
4 3
1 2
1 3
1 4
Sample Output 2:
NO

见题面

见题面