- Time limit: 1.00 s
- Memory limit: 512 MB
The first input line has two integers $n$ and $m$: the number of nodes and edges. The nodes are numbered $1,2,\dots,n$.
After this, there are $m$ lines describing the edges. Each line has two integers $a$ and $b$: there is an edge between nodes $a$ and $b$.
You may assume that there is at most one edge between each two nodes.
Print one integer: the girth of the graph. If there are no cycles, print $-1$.
- $1 \le n \le 2500$
- $1 \le m \le 5000$