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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
#define ll long long
#define pb push_back
using namespace std;
int N,M;
int Map[55][55];
int visit[55];
int main(){

    cin>>N>>M;
    for(int i = 1;i<=M;i++)
    {
        int a,b;
        cin>>a>>b;
        visit[a]++;
        visit[b]++;
        Map[a][b] = Map[b][a] = 1;
    }
    int sum = 0;
    int xi;
    bool falg = true;
    while(1)
    {
        falg = true;
        for(int i = 1;i<=N;i++)
        {
            if(visit[i]==1)
            {
                sum++;
                xi = i;
                falg = false;
                visit[i]--;
                break;
            }
        }
        if(falg) break;
        for(int i = 1;i<=N;i++)
        {
            if(Map[xi][i]==1)
                visit[i]--;
        }
    }
    cout<<sum<<endl;
    return 0;
}