#define Edge pair<int,int>
#define ff first
#define ss second
int cnt = 0,bcc_cnt = 0;
vector<int> G[MAXN],bcc[MAXN];
int pre[MAXN],low[MAXN],iscut[MAXN],bccno[MAXN];
stack<Edge> S;
void DFS(int u,int p)
{
    low[u] = pre[u] = ++cnt;
    int child = 0;
    for(auto v : G[u])
    {
        Edge e = {u,v};
        if(!pre[v])
        {
            S.push(e);
            child ++;
            DFS(v,u);
            low[u] = min(low[u],low[v]);
            if(low[v] >= pre[u])
            {
                iscut[u] = 1;
                bcc_cnt++;
                while(1)
                {
                    Edge x = S.top();S.pop();
                    if(bccno[x.ff] != bcc_cnt)
                    {
                      bccno[x.ff] = bcc_cnt;
                      bcc[bcc_cnt].push_back(x.ff);
                    }
                    if(bccno[x.ss] != bcc_cnt)
                    {
                      bccno[x.ss] = bcc_cnt;
                      bcc[bcc_cnt].push_back(x.ss);
                    }
                    if(x.ff == u && x.ss == v) break;
                }
            }
        }
        else if(pre[v] < pre[u] && v != p)
        {
            S.push(e);
            low[u] = min(low[u],pre[v]);
        }
    }
    if(p <= 0 && child == 1)
    {
        iscut[u] = 0;
    }
}