#include <cstdio>

#include <cstring>

#include <algorithm>

using namespace std;

const int N = 1e5, M = 1e5;

struct Edge {

    int v, next, idx;

    Edge(){}

    Edge(int _v, int _next, int _idx):

        v(_v), next(_next), idx(_idx){}

}e[M];

int dfn[N], deep, head[N], tot;

bool iscut[N], isbri[M];

void __init__()

{

    tot = deep = 0;

    memset(head, -1, sizeof(head));

    memset(dfn, 0, sizeof(dfn));

    memset(iscut, 0, sizeof(iscut));

    memset(isbri, 0, sizeof(isbri));

}

void add(int u, int v, int idx)

{

    e[tot] = Edge(v, head[u], idx);

    head[u] = tot++;

}

//lowi:i及其子孙通过回边所能走到的最早的祖先的dfn值

int dfs(int u, int fa)

{

    int lowu = dfn[u] = ++deep;//打上时间戳，并初始化low值

    int son = 0;//儿子数为0

    for(int i = head[u]; ~i; i = e[i].next) {

        int v = e[i].v;

        if(!dfn[v]) {//下一个点指向儿子

            son++;

            int lowv = dfs(v, u);

            lowu = min(lowu, lowv);

            if(lowv >= dfn[u]) iscut[u] = 1;//没有回边，是关节点

            if(lowv > dfn[u]) isbri[e[i].idx] = true;

        }

        else if(dfn[v] < dfn[u] && v != fa)//指向爷爷，发现回边

            lowu = min(lowu, dfn[v]);//利用回边来更新low值

    }

    if(fa == -1 && son == 1) iscut[u] = 0;//仅仅有1个儿子的根结点不是割顶

    return lowu;

}

int main()

{

    __init__();

    return 0;

}