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.



Sample input:
7 7
1 3
2 7
3 4
4 5
4 6
5 6
6 7


Sample output:
4

Submission status: Accepted

Solution code:
# -*- coding: utf-8 -*-
import copy

N,M = list(map(int, input().rstrip().split()))
AB_list = [list(map(int, input().rstrip().split())) for i in range(M)]
#-----

vertex_dic = { i: set() for i in range(1,N+1) }

for a,b in AB_list:
    vertex_dic[a].add(b)
    vertex_dic[b].add(a)

def check(c_vertex_dic :dict,c_start :int, c_end :int, passed :list):
# start→endへの経路が存在したらTrueを返す。
# ただし、start→endへの直接の経路は除く
    if c_start == c_end:
        return True
    
    for next in c_vertex_dic[c_start]:
        if next not in passed:
            passed.append(next)

            if check(c_vertex_dic, next, c_end, passed):
                return True
            


checked_dic = { i: set() for i in range(1,N+1) }  # check済みの経路を保存
cnt=0
for start in range(1,N+1):
    for end in vertex_dic[start]:
        if end not in checked_dic[start]:
            checked_dic[start].add(end)
            checked_dic[end].add(start)
            
            # 経路check用として、start→endへの直接の経路を削除したv_dicを用意
            v_dic = copy.deepcopy(vertex_dic)
            v_dic[start].remove(end)
            v_dic[end].remove(start)
        
            if not check(v_dic, start, end, [start]):
                cnt += 1
            
print(cnt)

Submission status: Accepted

Solution code:
def main():
    vertex, edge_num = map(int, input().split())
    edge = [[] for _ in range(vertex)]
    all_edge = []
    for _ in range(edge_num):
        all_edge.append(tuple(map(lambda x: int(x) - 1, input().split())))
        edge[all_edge[-1][0]].append(all_edge[-1][1])
        edge[all_edge[-1][1]].append(all_edge[-1][0])

    def search(exception):
        next_search = [0]
        has_searched = []
        result = 0
        while not next_search == []:
            now = next_search.pop(0)
            for d in edge[now]:
                if d in exception and now in exception:
                    continue
                elif d not in has_searched:
                    has_searched.append(d)
                    next_search.append(d)
                    result += 1
        return result == vertex

    answer = 0
    for ex in all_edge:
        if not search(ex):
            answer += 1
    print(answer)


if __name__ == '__main__':
    main()

Submission status: Accepted

Solution code:
from collections import deque
import sys
input = sys.stdin.readline
import bisect as bi
from operator import mul
from functools import reduce
import math

def readlines(n):
    for _ in range(n):
        a, b = map(int, input().split())
        yield a, b

def main():
    n, m = map(int, input().split())
    edges = list(readlines(m))

    graph = [set() for _ in range(n+1)]
    for a, b in edges:
        graph[a].add(b)
        graph[b].add(a)

    ans = 0
    for a, b in edges:
        queue = deque()
        queue.append(a)
        explored = set()
        explored.add(a)
        while queue:
            u = queue.popleft()
            for v in graph[u]:
                if (u, v) == (a, b) or v in explored:
                    continue
                explored.add(v)
                queue.append(v)

        ans += 0 if len(explored) == n else 1

    print(ans)
            

main()

Submission status: Accepted

Solution code:
def JOI14_B():
    N = I()
    A = [I()for _ in range(N)]
    A.extend(A)
    dp = [[0]*(N*2+1) for _ in range(N*2+1)]

    for j in range(N):
        for i in range(N*2-j):
            if (N-j)%2==1:
                dp[i][i+j] = max(dp[i+1][i+j]+A[i],dp[i][i+j-1]+A[i+j])
            else:
                if A[i]>A[i+j]:
                    dp[i][i+j] = dp[i+1][i+j]
                else:
                    dp[i][i+j] = dp[i][i+j-1]
    ans = 0
    for i in range(N):
        ans = max(ans,dp[i][i+N-1])
    print(ans)
    #print(dp)
    return

def square869120Contest1_G():
    def held_karp(dists,TL):
        # Copyright (c) 2016 Carl Ekerot
        """
        Implementation of Held-Karp, an algorithm that solves the Traveling
        Salesman Problem using dynamic programming with memoization.
        Parameters:
            dists: distance matrix
        Returns:
            A tuple, (cost, path).
        """
        n = len(dists)

        # Maps each subset of the nodes to the cost to reach that subset, as well
        # as what node it passed before reaching this subset.
        # Node subsets are represented as set bits.
        C = {}
        dp = defaultdict(int)

        # Set transition cost from initial state
        for k in range(1, n):
            C[(1 << k, k)] = (dists[0][k], 0)
            dp[(1 << k, k)] = 1

        # Iterate subsets of increasing length and store intermediate results
        # in classic dynamic programming manner
        for subset_size in range(2, n):
            for subset in itertools.combinations(range(1, n), subset_size):
                # Set bits for all nodes in this subset
                bits = 0
                for bit in subset:
                    bits |= 1 << bit
                shortest_length = inf
                # Find the lowest cost to get to this subset
                for k in subset:
                    prev = bits & ~(1 << k)

                    res = []
                    for m in subset:
                        if not (prev, m) in C:
                            continue
                        if m == 0 or m == k:
                            continue
                        if C[(prev, m)][0] + dists[m][k]>TL[m][k]:
                            continue
                        res.append((C[(prev, m)][0] + dists[m][k], m))
                        if shortest_length>C[(prev, m)][0] + dists[m][k]:
                            shortest_length = C[(prev, m)][0] + dists[m][k]
                    if not res:
                        continue
                    C[(bits, k)] = min(res)
                    for d,m in res:
                        if shortest_length!=d:
                            continue
                        dp[(bits, k)] += dp[(prev,m)]

        # We're interested in all bits but the least significant (the start state)
        bits = (2 ** n - 1) - 1

        # Calculate optimal cost
        res = []
        shortest_length = inf
        for k in range(1, n):
            if not (bits, k) in C:
                continue
            if C[(bits, k)][0] + dists[k][0] > TL[k][0]:
                continue
            res.append((C[(bits, k)][0] + dists[k][0], k))
            if shortest_length > C[(bits, k)][0] + dists[k][0]:
                shortest_length = C[(bits, k)][0] + dists[k][0]
        if not res:
            return False
        opt, parent = min(res)
        way = 0
        for d, k in res:
            if not (bits, k) in C:
                continue
            if C[(bits, k)][0] + dists[k][0] > TL[k][0]:
                continue
            if shortest_length < d:
                continue
            way += dp[(bits,k)]

        # Backtrack to find full path
        path = []
        for i in range(n - 1):
            path.append(parent)
            new_bits = bits & ~(1 << parent)
            _, parent = C[(bits, parent)]
            bits = new_bits

        # Add implicit start state
        path.append(0)

        return shortest_length, list(reversed(path)), way

    N, M = LI()
    dist = [[inf]*N for _ in range(N)]
    TL = [[0]*N for _ in range(N)]
    for _ in range(M):
        s, t, d, time = LI()
        s -= 1; t -= 1
        dist[s][t] = dist[t][s] = d
        TL[s][t] = TL[t][s] = time
    ans = held_karp(dist,TL)
    if (not ans) or ans[2]==0:
        print("IMPOSSIBLE")
        return
    print(ans[0],ans[2])
    return

def JOI13_D():
    def solve(yday,leader,next):
        a = [0]*3
        for i in range(3):
            if next&(1<<i)==(1<<i):
                a[i] = 1
        rep = 0
        if a[leader]==0:
            return rep
        for i in range(3):
            if yday&(1<<i)==(1<<i):
                if a[i]==1:
                    rep = 1
        return rep
    N = I()
    S = SI()
    member = {"J":0,"O":1,"I":2}
    dp = [[0]*8 for _ in range(N+1)]
    dp[0][1] = 1
    for i in range(N):
        leader = member[S[i]]
        for j in range(8):
            for k in range(8):
                dp[i+1][j] += (dp[i][k]*solve(k,leader,j))
    ans = sum(dp[-1])%10007
    #print(dp)
    print(ans)
    return

def JOI16_D():
    N, M = LI()
    A = [(I()-1)for _ in range(N)]
    imos = [[0] * (N + 1) for _ in range(M)]
    for i in range(M):
        for j in range(N):
            imos[i][j + 1] += imos[i][j] + (A[j] != i)
    loop = 2**M
    dp = [inf]*loop
    dp[0] = 0
    cnt = Counter(A)
    L = [0]*loop
    #print(imos)
    for i in range(loop):
        for j in range(M):
            if i&(1<<j)==(1<<j):
                continue
            next = i|(1<<j)
            if L[next]==0:
                L[next] = L[i]+cnt[j]
            cur = imos[j][L[next]] - imos[j][L[i]]
            if dp[next]>dp[i] + cur:
                dp[next] = dp[i] + cur
    ans = dp[-1]
    #print(L)
    print(ans)
    return

def ABC6_D():
    N = I()
    C = [I() for _ in range(N)]
    LIS = [C[0]]
    for i in range(N):
        if C[i] > LIS[-1]:
            LIS.append(C[i])
        else:
            LIS[bisect.bisect_left(LIS, C[i])] = C[i]
    print(N - len(LIS))
    return

def ABC134_E():
    N = I()
    A = [I()for _ in range(N)]
    que = deque()
    que.append(A[0])
    L = 1
    for i in range(1,N):
        cur = bisect.bisect_left(que,A[i])
        #print(que,cur,L)
        if cur==0:
            que.appendleft(A[i])
            L += 1
        else:
            que[cur-1] = A[i]

    #print(que)
    ans = len(que)
    print(ans)

    return

def JOI7_F():
    def dijkstra_2(edge_adj, node, start):
        # node<=2000くらい
        # edge_adj[node][to] = [cost]
        dist = [inf] * node
        used = [False] * node
        dist[start] = 0
        while True:
            v = -1
            for i in range(node):
                if not used[i] and (v == -1 or dist[v] > dist[i]):
                    v = i
            if v == -1:
                break
            used[v] = True
            for i in range(node):
                if dist[i] > dist[v] + edge_adj[v][i]:
                    dist[i] = dist[v] + edge_adj[v][i]
        return dist
    N, K = LI()
    V = [[inf]*N for _ in range(N)]
    ans = []
    for _ in range(K):
        A = LI()
        s = A[1]-1
        t = A[2]-1
        if A[0]==1:
            if V[s][t] <= A[3]:
                continue
            V[s][t] = A[3]
            V[t][s] = A[3]
        else:
            dist = dijkstra_2(V,N,s)
            ans.append(dist[t])
    for v in ans:
        if v==inf:
            print(-1)
            continue
        print(v)
    return

def JOI15_E():
    def bfs(n, E, fordfs):
        # 点の数、スタートの点、有向グラフ
        W = [inf] * n
        # 各点の状態量、最短距離とか,見たかどうかとか
        que = deque()
        for e in E:
            e -=1
            W[e] = 0
            que.append(e)
        while que:
            now = que.popleft()
            nowW = W[now]
            for ne in fordfs[now]:
                if W[ne] > nowW + 1:
                    W[ne] = nowW + 1
                    que.append(ne)
        return W

    class Dijkstra(object):
        """
        construct: O(ElogV)
        """

        def __init__(self, edges, start=0):
            """
            :param list of list of list of int edges:
            :param int start=0:
            """
            self.__dist = [inf] * len(edges)
            self.__dist[start] = 0
            self.__calculate(edges, start)

        @property
        def dist(self):
            return self.__dist

        def __calculate(self, edges, start):
            Q = [(0, start)]  # (dist,vertex)
            while (Q):
                dist, v = heapq.heappop(Q)
                if self.dist[v] < dist: continue  # 候補として挙がったd,vだが、他に短いのがある
                for u, cost in edges[v]:
                    if self.dist[u] > self.dist[v] + cost:
                        self.__dist[u] = self.dist[v] + cost
                        heapq.heappush(Q, (self.dist[u], u))
    N, M, K, S = LI()
    P, Q = LI()
    C = [I()for _ in range(K)]
    V = [[]for _ in range(N)]
    for _ in range(M):
        s, t = LI()
        s -= 1
        t -= 1
        V[s].append(t)
        V[t].append(s)
    L = bfs(N,C,V)
    #print(L)
    cost = [[]for _ in range(N)]
    for i in range(N):
        for v in V[i]:
            if L[v]==0:
                continue
            elif L[v]<=S:
                cost[i].append((v,Q))
            else:
                cost[i].append((v,P))
    di = Dijkstra(cost)
    ans = di.dist
    #print(cost)
    if L[-1]<=S:
        print(ans[N-1]-Q)
    else:
        print(ans[N-1]-P)
    return

def JOI13_E():
    def bfs(n, e, fordfs):
        # 点の数、スタートの点、有向グラフ
        W = [inf] * n
        # 各点の状態量、最短距離とか,見たかどうかとか
        W[e] = 0
        que = deque()
        que.append(e)
        while que:
            now = que.popleft()
            nowW = W[now]
            for ne in fordfs[now]:
                if W[ne] == inf:
                    W[ne] = nowW + 1
                    que.append(ne)
        return W

    def dijkstra_2(edge_adj, node, start):
        # node<=2000くらい
        # edge_adj[node][to] = [cost]
        dist = [inf] * node
        used = [False] * node
        dist[start] = 0
        while True:
            v = -1
            for i in range(node):
                if not used[i] and (v == -1 or dist[v] > dist[i]):
                    v = i
            if v == -1:
                break
            used[v] = True
            for i in range(node):
                if dist[i] > dist[v] + edge_adj[v][i]:
                    dist[i] = dist[v] + edge_adj[v][i]
        return dist
    N, K = LI()
    C = [[]for _ in range(N)]
    V = [[]for _ in range(N)]
    for i in range(N):
        C[i] = LI()
    for i in range(K):
        a, b = LI()
        a -= 1
        b -= 1
        V[a].append(b)
        V[b].append(a)
    costV = [[inf]*N for _ in range(N)]
    for i in range(N):
        L = bfs(N,i,V)
        c = C[i][0]; l = C[i][1]
        for j in range(N):
            if i==j:
                continue
            if L[j]<=l:
                costV[i][j] = c
    dist = dijkstra_2(costV,N,0)
    ans = dist[N-1]
    #print(costV)
    print(ans)
    return

def ABC12_D():
    def warshall_floyd(n, d):
        # d[i][j]: iからjへの最短距離
        for k in range(n):
            for i in range(n):
                for j in range(n):
                    d[i][j] = min(d[i][j], d[i][k] + d[k][j])
        return d
    N, M = LI()
    V = [[inf]*N for _ in range(N)]
    for i in range(N):
        V[i][i] = 0
    for _ in range(M):
        a, b, t = LI()
        a -= 1
        b -= 1
        V[a][b] = t
        V[b][a] = t
    L = warshall_floyd(N,V)
    #print(L)
    ans = inf
    for i in range(N):
        cur = max(L[i])
        ans = min(ans,cur)
    print(ans)
    return

def ABC79_D():
    def warshall_floyd(n, d):
        # d[i][j]: iからjへの最短距離
        for k in range(n):
            for i in range(n):
                for j in range(n):
                    d[i][j] = min(d[i][j], d[i][k] + d[k][j])
        return d
    H, W = LI()
    C = [LI()for _ in range(10)]
    A = [LI()for _ in range(H)]
    L = warshall_floyd(10,C)
    #print(L)
    ans = 0
    for a in A:
        for i in a:
            if i>=0:
                ans += L[i][1]
    print(ans)
    return

def JOIgassyuku10_3():
    N, M, K = LI()
    V = [[]for _ in range(N)]
    for _ in range(M):
        a, b, c = LI()
        a -= 1
        b -= 1
        V[a].append((b,c))
        V[b].append((a,c))


    return

def ABC74_D():
    def warshall_floyd(n, d):
        # d[i][j]: iからjへの最短距離
        for k in range(n):
            for i in range(n):
                for j in range(n):
                    d[i][j] = min(d[i][j], d[i][k] + d[k][j])
        return d
    N = I()
    A = [LI() for _ in range(N)]
    dist = warshall_floyd(N,copy.deepcopy(A))
    shortest_path = 0
    for i in range(N):
        for j in range(N):
            if i==j:
                continue
            if dist[i][j]<A[i][j]:
                print(-1)
                return
            if dist[i][j]>A[i][j]:
                continue
            flag = True
            for k in range(N):
                if i==k or j==k:
                    continue
                judge = (dist[i][k]+dist[k][j])-dist[i][j]
                if judge==0:
                    flag = False
            if flag:
                shortest_path += A[i][j]
    ans = shortest_path//2
    print(ans)
    return

def ABC65_D():
    class Kruskal_UnionFind():
        # 無向グラフであるという前提に注意
        def __init__(self, N):
            self.edges = []
            self.rank = [0] * N
            self.par = [i for i in range(N)]
            self.counter = [1] * N

        def add(self, u, v, d):
            """
            u = from, v = to, d = cost
            """
            self.edges.append([u, v, d])

        def find(self, x):
            if self.par[x] == x:
                return x
            else:
                self.par[x] = self.find(self.par[x])
                return self.par[x]

        def unite(self, x, y):
            x = self.find(x)
            y = self.find(y)
            if x != y:
                z = self.counter[x] + self.counter[y]
                self.counter[x], self.counter[y] = z, z
            if self.rank[x] < self.rank[y]:
                self.par[x] = y
            else:
                self.par[y] = x
                if self.rank[x] == self.rank[y]:
                    self.rank[x] += 1

        def size(self, x):
            x = self.find(x)
            return self.counter[x]

        def same(self, x, y):
            return self.find(x) == self.find(y)

        def Kruskal(self):
            """
            return: 最小全域木のコストの和
            """
            edges = sorted(self.edges, key=lambda x: x[2])  # costでself.edgesをソートする
            res = 0
            for e in edges:
                if not self.same(e[0], e[1]):
                    self.unite(e[0], e[1])
                    res += e[2]
            return res
    N = I()
    X = []
    for i in range(N):
        a, b = LI()
        X.append((a,b))
    P = defaultdict(set)
    for i,x in enumerate(X):
        P[x] = i
    graph = Kruskal_UnionFind(N + 1)

    X.sort(key=lambda x:x[0])
    for i in range(N-1):
        if X[i+1][0]-X[i][0]>abs(X[i+1][1]-X[i][1]):
            continue
        r = X[i+1][0]-X[i][0]
        graph.add(P[X[i]], P[X[i+1]], r)

    X.sort(key=lambda x:x[1])
    for i in range(N-1):
        if X[i+1][1]-X[i][1]>abs(X[i+1][0]-X[i][0]):
            continue
        r = X[i+1][1]-X[i][1]
        graph.add(P[X[i]], P[X[i+1]], r)

    ans = graph.Kruskal()
    print(ans)
    return

def ABC84_D():
    def is_prime(n):
        if n == 1: return False
        for k in range(2, int(math.sqrt(n)) + 1):
            if n % k == 0:
                return False
        return True

    def like_2017(x):
        if is_prime(x) and is_prime(x//2+1):
            return True
        return False

    Q = I()
    maxX = 10**5
    imos = [0]*(maxX+1)
    for i in range(maxX+1):
        if like_2017(i) and i!=2:
            imos[i] = imos[i-1] + 1
        else:
            imos[i] = imos[i - 1]
    L = [LI()for _ in range(Q)]
    ans = []
    for l,r in L:
        cur = imos[r]-imos[l-1]
        ans.append(cur)
    for v in ans:
        print(v)
    return

def square869120Contest1_E():
    N, Q = LI()
    A = LI()
    C = LI()
    C.append(1)
    L = [0]*N
    for i in range(1,N):
        L[i] = pow(A[i-1],A[i],mod) + L[i-1]
    #print(L)
    ans = 0
    now = 0
    for i in range(Q+1):
        next = C[i]-1
        cur = abs(L[next]-L[now])
        ans += cur
        ans %= mod
        now = next
        #print(ans)
    print(ans)
    return

def ABC34_C():
    # rが小さい時
    def cmb(n, r, mod):
        cur = 1
        for i in range(r):
            cur *= (n-i)
            cur %= mod
        for i in range(r):
            cur *= pow(i+1,mod-2,mod)
            cur %= mod
        return cur

    W, H = LI()
    r = W+H-2; l = H-1
    ans = cmb(r,l,mod)
    print(ans)
    return

def ABC145_D():
    def cmb(n, r, mod):
        cur = 1
        for i in range(r):
            cur *= (n-i)
            cur %= mod
        for i in range(r):
            cur *= pow(i+1,mod-2,mod)
            cur %= mod
        return cur

    X, Y = LI()
    if (X+Y)%3!=0:
        print(0)
        return
    r = (X+Y)//3; l = X-(X+Y)//3
    if l<0:
        print(0)
        return
    ans = cmb(r,l,mod)
    print(ans)
    return

def ABC21_D():
    def cmb(n, r, mod):
        cur = 1
        for i in range(r):
            cur *= (n-i)
            cur %= mod
        for i in range(r):
            cur *= pow(i+1,mod-2,mod)
            cur %= mod
        return cur

    N = I()
    K = I()
    r = N+K-1; l = K
    ans = cmb(r,l,mod)
    print(ans)
    return

def ABC149_F():
    # 子の数のカウント
    def dfs(n,s,edges,children):
        cur = 1
        children[s] = 0
        for i in edges[s]:
            if children[i]!=-1:
                continue
            children[i] = True
            now,children = dfs(n,i,edges,children)
            cur += now
        children[s] = cur
        return cur,children
    N = I()
    V = [[]for _ in range(N)]
    for _ in range(N-1):
        a, b = LI()
        a -= 1; b -= 1
        V[a].append(b)
        V[b].append(a)
    children = [-1]*N
    C = dfs(N,0,V,children)[1]
    #print(C)

    # 頂点数の期待値計算
    inv = pow(2, mod - 2, mod)
    ans = 1
    p = [pow(inv, i, mod) for i in range(N)]
    for i in range(1,N):
        c = C[i]
        d = N-c
        cur = (1-p[c])*(1-p[d])
        ans += cur
        ans %= mod
    ans -= N * inv
    # 全部白なら+１がない
    ans -= pow(inv,N,mod)

    ans += mod
    ans %= mod
    print(ans)
    return

def NIKKEI2019_A():
    N = I()
    A = LI()
    S = [0]*(N+1)
    for i in range(N):
        S[i+1] = A[i]+S[i]
    ans = []
    for k in range(1,N+1):
        cur = 0
        for i in range(N-k+1):
            now = S[i+k]-S[i]
            if cur<now:
                cur = now
        ans.append(cur)
    for v in ans:
        print(v)
    return

def JOI10_A():
    N, M = LI()
    L = [I()for _ in range(N-1)]
    A = [I()for _ in range(M)]
    S = [0]*N
    for i in range(N-1):
        S[i+1] = S[i] + L[i]
    #print(S)
    ans = 0
    now = 0
    for i in range(M):
        #print(now)
        ans += abs(S[A[i]+now] - S[now])
        now += A[i]
    print(ans%100000)
    return

"""
7 5 
2 
1 
1 
3 
2 
1 
2
-1 
3 
2
-3
"""

def JOI11_1():
    N, M = LI()
    K = I()
    F = [SI()for _ in range(N)]
    A = [LI()for _ in range(K)]
    CJ = [[0]*(M+1) for _ in range(N+1)]
    CO = [[0]*(M+1) for _ in range(N+1)]
    CI = [[0]*(M+1) for _ in range(N+1)]
    for i in range(N):
        nowj = 0
        nowo = 0
        nowi = 0
        for j in range(M):
            if F[i][j]=="J":
                nowj += 1
            CJ[i+1][j+1] = CJ[i][j+1] + nowj
            if F[i][j]=="O":
                nowo += 1
            CO[i+1][j+1] = CO[i][j+1] + nowo
            if F[i][j]=="I":
                nowi += 1
            CI[i+1][j+1] = CI[i][j+1] + nowi
    ans = []
    for a,b,c,d in A:
        curj = CJ[c][d]-CJ[c][b-1]-CJ[a-1][d]+CJ[a-1][b-1]
        curo = CO[c][d]-CO[c][b-1]-CO[a-1][d]+CO[a-1][b-1]
        curi = CI[c][d]-CI[c][b-1]-CI[a-1][d]+CI[a-1][b-1]
        ans.append((curj,curo,curi))

    for v in ans:
        print(" ".join(map(str,v)))
    return

"""
4 7 
4 
JIOJOIJ 
IOJOIJO 
JOIJOOI 
OOJJIJO 
3 5 4 7 
2 2 3 6 
2 2 2 2 
1 1 4 7

"""
def ABC106_D():
    N, M, Q = LI()
    A = [[0]*(N) for _ in range(N)]
    S = [[0]*(N+1) for _ in range(N+1)]
    for _ in range(M):
        l, r = LI()
        A[l-1][r-1] += 1
    for i in range(N):
        now = 0
        for j in range(N):
            now += A[i][j]
            S[i+1][j+1] = S[i][j+1]+now
    ans = []
    for _ in range(Q):
        p, q = LI()
        cur = S[q][q] - S[p-1][q] - S[q][p-1] + S[p-1][p-1]
        ans.append(cur)
    for v in ans:
        print(v)
    return

def gigacode2019_D():
    H, W, K, V = LI()
    A = [LI()for _ in range(H)]
    S = [[0]*(W+1)for _ in range(H+1)]
    for h in range(H):
        now = 0
        for w in range(W):
            now += (A[h][w] + K)
            S[h+1][w+1] = S[h][w+1] + now
    ans = 0
    for h in range(H):
        for w in range(W):
            for i in range(h,H+1):
                l = w; r = W+1
                while(r-l>1):
                    now = (r+l)//2
                    cur = S[i][now] - S[i][w] - S[h][now] + S[h][w]
                    if cur<=V:
                        l = now
                    else:
                        r = now
                c = (i-h)*(l-w)
                if ans<c:
                    ans = c
    print(ans)
    return

def ABC14_C():
    N = I()
    colors = 10**6+1
    imos = [0]*(colors+2)
    for _ in range(N):
        a, b = LI()
        imos[a] += 1
        imos[b+1] -= 1
    ans = 0
    cur = 0
    for i in range(colors):
        cur += imos[i]
        if ans<cur:
            ans = cur
    print(ans)
    return

def JOI14_A():
    N, M = LI()
    P = LI()
    A = [0]*(N-1); B = [0]*(N-1); C = [0]*(N-1)
    for i in range(N-1):
        A[i], B[i], C[i] = LI()
    imos = [0]*N
    prev = P[0]
    for p in P[1:]:
        if prev<p:
            imos[prev - 1] += 1
            imos[p-1] -= 1
        else:
            imos[p - 1] += 1
            imos[prev-1] -= 1
        prev = p
    cur = imos[0]
    for i in range(N-1):
        cur += imos[i+1]
        imos[i+1] = cur
    #print(imos)
    ans = 0
    for i in range(N-1):
        cur = imos[i]
        ans += min(A[i]*cur,B[i]*cur+C[i])
    print(ans)
    return

def JOI11_4():
    N, M = LI()
    imos = [[0]*(N+2) for _ in range(N+2)]
    for _ in range(M):
        a, b, x = LI()
        imos[a-1][b-1] += 1
        imos[a-1][b] -= 1
        imos[a+x][b-1] -= 1
        imos[a+x+1][b] += 1
        imos[a+x][b+x+1] += 1
        imos[a+x+1][b+x+1] -= 1
    #for v in imos:
    #    print(v)
    for h in range(N+1):
        for i in range(N):
            imos[h][i+1] += imos[h][i]
    for w in range(N+1):
        for i in range(N):
            imos[i+1][w] += imos[i][w]
    #print()
    #for v in imos:
    #    print(v)
    for h in range(N+1):
        for i in range(N):
            imos[h+1][i+1] += imos[h][i]
    ans = 0
    #for v in imos:
    #    print(v)
    for h in range(N):
        for w in range(h+1):
            if imos[h][w]<=0:
                continue
            ans += 1
    print(ans)
    return
"""
5 2
2 2 1
2 1 3
"""
def ABC75_C():
    # https://tjkendev.github.io/procon-library/python/graph/bridge.html
    def bridge_finding(G, N, start=0):
        fin = [False] * N
        v_cnts = [0] * N
        used = [False] * N
        bG = [[] for i in range(N)]  # 縮約後のグラフ
        bV = [[] for i in range(N)]  # 各ノードに縮約される元頂点

        def dfs(v, prev, edges, conts):
            cur_c = prev_c = 0
            used[v] = True
            conts.append(v)
            for w in G[v]:
                if used[w]:
                    if w == prev:
                        # (v, prev)の多重辺対応
                        if prev_c == 1:
                            v_cnts[prev] -= 1
                            cur_c += 1
                        prev_c += 1
                    elif not fin[w]:
                        v_cnts[w] -= 1
                        cur_c += 1
                else:
                    w_edges = [];
                    w_conts = []
                    ret = dfs(w, v, w_edges, w_conts)
                    if ret > 0:
                        edges += w_edges
                        conts += w_conts
                    else:
                        # (v, w)は橋
                        bG[w] = w_edges
                        for u in w_edges:
                            bG[u].append(w)
                        bV[w] = w_conts
                        edges.append(w)
                    cur_c += ret
            fin[v] = True
            cur_c += v_cnts[v]
            return cur_c

        dfs(start, -1, bG[start], bV[start])
        for u in bG[start]:
            bG[u].append(start)
        return bG  # , bV

    N, M = LI()
    V = [[]for _ in range(N)]
    for _ in range(M):
        a, b = LI()
        a -= 1; b -= 1
        V[a].append(b)
        V[b].append(a)
    cur = bridge_finding(V,N)
    ans = 0
    for v in cur:
        ans += len(v)
    ans //=2
    print(ans)
    return

import sys,copy,bisect,itertools,heapq,math,random
from heapq import heappop,heappush,heapify
from collections import Counter,defaultdict,deque

def I(): return int(sys.stdin.readline())
def LI(): return list(map(int,sys.stdin.readline().split()))
def LSI(): return list(map(str,sys.stdin.readline().split()))
def LS(): return sys.stdin.readline().split()
def SI(): return sys.stdin.readline().strip()
global mod,mod2,inf,alphabet,_ep
mod = 10**9 + 7
mod2 = 998244353
inf = 10**18
_ep = 10**(-12)
alphabet = [chr(ord('a') + i) for i in range(26)]

sys.setrecursionlimit(10**6)

if __name__ == '__main__':
    ABC75_C()
"""

"""

Submission status: Accepted

Solution code:
def main():
    from collections import deque

    def traversal(ignore_idx):
        s = 0
        visited = [-1] * N
        visited[s] = 0

        dq = deque([s])
        while dq:
            v = dq.popleft()
            for u, edge_idx in g[v]:
                if ~visited[u] or edge_idx == ignore_idx:
                    continue
                dq.append(u)
                visited[u] = 0
        return all(~flg for flg in visited)  # 連結ならTrue

    N, M = map(int, input().split())
    g = tuple(set() for _ in range(N))
    for edge_idx in range(M):
        a, b = (int(x) - 1 for x in input().split())
        g[a].add((b, edge_idx))
        g[b].add((a, edge_idx))

    ret = 0
    for ignore_idx in range(M):
        res = traversal(ignore_idx)
        if not res:
            ret += 1
    print(ret)


if __name__ == '__main__':
    main()