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 Ruby (2.3.3) (judge verdict: Accepted)

# Your code here!
n,m=gets.split
n=n.to_i
m=m.to_i

array4=[]
m.times{
    
    array4<<gets.split.map(&:to_i)}
answer=0
jj=0
m.times{
array=array4-[array4[jj]]

array2=Array.new(n,0)
array3=Array.new(n,1)
m.times{
i=0
(m-1).times{
    
    if i==0
    array2[array[i][0]-1]=1
     array2[array[i][1]-1]=1
     
 elsif   array2[array[i][0]-1]==0 && array2[array[i][1]-1]==0
        array2[array[i][0]-1]=2
        array2[array[i][1]-1]=2
   elsif    array2[array[i][0]-1]==1 || array2[array[i][1]-1]==1
       array2[array[i][0]-1]=1
        array2[array[i][1]-1]=1
        
    else array2[array[i][0]-1]=2
        array2[array[i][1]-1]=2
 end
 i+=1
    
 
}

if  array2==array3
    break
end

}
if array2!=array3
    answer+=1
end
jj+=1

}

puts answer