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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System.Collections.Generic;
using System.Linq;
using System;
class Program
{
    static void Main()
    {
        string[] a = Console.ReadLine().Split(' ');
        int[] b = new int[2];
        b[0] = int.Parse(a[0]);//Vert
        b[1] = int.Parse(a[1]);//Line

        List<int>[] vertList = new List<int>[b[0]];
        for (int i = 0; i < b[0]; i++){
            vertList[i] = new List<int>();
        }

        for (int i = 0; i < b[1]; i++){
            string[] c = Console.ReadLine().Split(' ');
            int[] d = new int[2];
            d[0] = int.Parse(c[0]) - 1;
            d[1] = int.Parse(c[1]) - 1;
            vertList[d[0]].Add(d[1]);
            vertList[d[1]].Add(d[0]);
        }

        int bridgeCount = 0;
        bool flag = true;
        while (flag)
        {
            flag = false;
            for (int i = 0; i < b[0]; i++)
            {
                if (vertList[i].Count() == 1)
                {
                    bridgeCount++;
                    int dest = vertList[i][0];
                    vertList[dest].Remove(i);
                    vertList[i].RemoveAt(0);
                    flag = true;
                }
            }
        }

        Console.WriteLine(bridgeCount.ToString());
    }
}