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;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp95 {
    class Program {
        static void Main(string[] args) {
            var st = Console.ReadLine().Split().Select(int.Parse).ToArray();
            int N = st[0];
            int M = st[1];
            var a = new int[M];
            var b = new int[M];

            var tupleList = new List<Tuple<int, int>>();

            for (int i = 0; i < M; i++) {
                var x = Console.ReadLine().Split().Select(int.Parse).ToArray();
                a[i] = x[0];
                b[i] = x[1];
                tupleList.Add(new Tuple<int, int>(a[i], b[i]));
            }

            int ans = 0;

            tupleList.Sort((p, q) => p.Item1.CompareTo(q.Item1));

            int before_cnt = 0;

            for (int i = 0; i < M; i++) {
                var already = new List<int> { };
                already.Add(tupleList[i].Item1);

                var check = Enumerable.Repeat(0, M).ToArray();

                while (true) {
                    before_cnt = already.Count();

                    for (int j = 0; j < M; j++) {
                        if (i == j) {
                            continue;
                        }

                        if (check[j] == 0 && already.Contains(tupleList[j].Item1)) {
                            already.Add(tupleList[j].Item2);
                            check[j] = 1;
                        } else if (check[j] == 0 && already.Contains(tupleList[j].Item2)) {
                            already.Add(tupleList[j].Item1);
                            check[j] = 1;
                        }
                        


                    }

                    if (before_cnt == already.Count()) {
                        break;
                    }
                }
                
                if (already.Distinct().Count() != N) {
                    ans++;
                }





            }
            Console.WriteLine(ans);
        }
    }
}