Problem:
Score : 300 points

Problem Statement

You are given an undirected connected graph with N vertices and M edges that does not contain self-loops and double edges.

The i-th edge (1 \leq i \leq M) connects Vertex a_i and Vertex b_i.

An edge whose removal disconnects the graph is called a bridge.

Find the number of the edges that are bridges among the M edges.

Notes

A self-loop is an edge i such that a_i=b_i (1 \leq i \leq M).

Double edges are a pair of edges i,j such that a_i=a_j and b_i=b_j (1 \leq i<j \leq M).

An undirected graph is said to be connected when there exists a path between every pair of vertices.

Constraints

2 \leq N \leq 50

N-1 \leq M \leq min(N(N−1)⁄2,50)

1 \leq a_i<b_i \leq N

The given graph does not contain self-loops and double edges.

The given graph is connected.

Input

Input is given from Standard Input in the following format:

N M
a_1 b_1
a_2 b_2
:
a_M b_M

Output

Print the number of the edges that are bridges among the M edges.

Sample Input 1

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

Sample Output 1

4

The figure below shows the given graph:

The edges shown in red are bridges. There are four of them.

Sample Input 2

3 3
1 2
1 3
2 3

Sample Output 2

0

It is possible that there is no bridge.

Sample Input 3

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

Sample Output 3

5

It is possible that every edge is a bridge.

Solution in Scala (2.11.7) (judge verdict: Wrong Answer)

object Main extends App {
	val nm = scala.io.StdIn.readLine.split(" ").map(_.toInt)
	var edges = List[(Int,Int)]()

	for(i<-0 until nm(1)){
		val temp = scala.io.StdIn.readLine.split(" ").map(_.toInt)
		edges = (temp(0), temp(1)) :: edges
	}

	def check(t: Int, x: List[(Int,Int)]): Boolean = {
		val a = x.head
		var re = Set(a._1, a._2)
		var te = x.tail

		for(i<- te){
			if(re.contains(i._1) || re.contains(i._2)){
				re = re + i._1 + i._2
			}
		}

		re.size == t
	}

	var answer = 0
	for(x <- edges){
			if(! check(nm(0), edges.filter(_ != x))){
				answer += 1
			}
	}

	println(answer)
}