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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;

class Main{
    public static void main(String[]args){
		Scanner sc = new Scanner(System.in);
		String ssc = sc.nextLine();
		String[] assc = ssc.split(" ");
		int inn = Integer.parseInt(assc[0]);
		int inm = Integer.parseInt(assc[1]);
		int[][] iainn = new int[inn][inn];
		int sil = 0;
		int sir = 0;
		int retcount = 0;
		int retflag = 0;
		String[] siroot = new String[inm];
		for(int i=0;i<inn;i++){
			for(int j=0;j<inn;j++){
				iainn[i][j] = 1000;
			}
		}
		for(int i=0;i<inm;i++){
			ssc = sc.nextLine();
			siroot[i] = ssc;
		}
		for(int ing=0;ing<inm;ing++){
			for(int i=0;i<inm;i++){
				if(ing==i){
					continue;
				}
				ssc = siroot[i];
				assc = ssc.split(" ");
				sil = Integer.parseInt(assc[0]);
				sir = Integer.parseInt(assc[1]);
				sil--;
				sir--;
				iainn[sil][sir] = 1;
				iainn[sir][sil] = 1;
			}
			for(int x=0;x<inn;x++){
				for(int y=0;y<inn;y++){
					for(int z=0;z<inn;z++){
						if(iainn[y][z] > iainn[y][x] + iainn[x][z]){
							iainn[y][z] = iainn[y][x] + iainn[x][z];
						}
					}
				}
			}
			for(int j=0;j<inn;j++){
				for(int k=0;k<inn;k++){
					if(j==k){
						continue;
					}
					else if(iainn[j][k]>=1000){
						retflag++;
					}
					else{
						iainn[j][k] = 1000;
					}
				}
			}
			if(retflag!=0){
				retcount++;
				retflag = 0;
			}
		}
		System.out.println(retcount);
    }
}