Competitions

# DFS. Articulation points. Bridges

# Bridges

The undirected graph is given. Find all its bridges.

#### Input

The first line contains two positive integers **n** and **m** (**n** ≤ **20000**, **m** ≤ **200000**) - the number of vertices and edges in a graph respectively. Each of the next **m** lines contains the description of one edge. The edge number **i** is described with two positive integers `b`

, _{i}`e`

(_{i}**1** ≤ `b`

, _{i}`e`

≤ _{i}**n**) - the numbers of the vertices it connects.

#### Output

Print in the first line the number **b** of bridges in a given graph. Print on the next line **b** integers - the edge numbers that are bridges, in increasing order. The edges are numbered from one in the order they are given at the input.

Input example #1

6 7 1 2 2 3 3 4 1 3 4 5 4 6 5 6

Output example #1

1 3