#include<vector>
#include<algorithm>
#define N 1005
struct edge{
	int u,v;
	bool is_bridge;
	edge(int u=0,int v=0):u(u),v(v),is_bridge(0){}
};
std::vector<edge> E;
std::vector<int> G[N];// 1-base
int low[N],vis[N],Time,bridge_cnt;
inline void add_edge(int u,int v){
	G[u].push_back(E.size());
	E.push_back(edge(u,v));
	G[v].push_back(E.size());
	E.push_back(edge(v,u));
}
void dfs(int u,int re=-1){//u當前點，re為u連接前一個點的邊 
	int v;
	low[u]=vis[u]=++Time;
	st[top++]=u;
	for(size_t i=0;i<G[u].size();++i){
		int e=G[u][i];v=E[e].v;
		if(!vis[v]){
			dfs(v,e^1);//e^1反向邊 
			low[u]=std::min(low[u],low[v]);
			if(vis[u]<low[v]){
				E[e].is_bridge=E[e^1].is_bridge=1;
				++bridge_cnt;
			}
		}else if(vis[v]<vis[u]&&e!=re)
			low[u]=std::min(low[u],vis[v]);
	}
}