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 (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
int connect[51][51]={0};
int visited[51]={0},n;
int dfs(int a){
    visited[a]=1;
    for(int i=1;i<=n;i++){
        if(connect[a][i]==1&&visited[i]==0){
            dfs(i);
        }
    }
}
int main()
{   int m;
    scanf("%d%d",&n,&m);
    int a[m],b[m];
    for(int i=0;i<m;i++){
        scanf("%d%d",&a[i],&b[i]);
        connect[a[i]][b[i]]++;
        connect[b[i]][a[i]]++;
    }
    int ans=0;
    for(int i=0;i<m;i++){
        for(int j=1;j<=n;j++){
            visited[j]=0;
        }
        connect[a[i]][b[i]]=0;
        connect[b[i]][a[i]]=0;
        dfs(1);
        for(int j=1;j<=n;j++){
            if(visited[j]==0){
                ans++;
                break;
            }
        }
        connect[a[i]][b[i]]=1;
        connect[b[i]][a[i]]=1;
    }
    printf("%d",ans);
    return 0;
}