const int nsz=100050,msz=200050;
struct te{int t,pr;}edge[msz]; //无向图: msz*2
int hd[nsz],pe=1,in[nsz];
void adde(int f,int t,int v){edge[++pe]=(te){t,hd[f],v};hd[f]=pe;}
void adddb(int f,int t,int v){adde(f,t,v);adde(t,f,v);}

int ts[nsz],pt=0;
bool topsort(){
    rep(i,1,n)if(in[i]==0)que[++qt]=i,ts[++pt]=i;
    while(qh<=qt){
        int u=que[qh++];
        for(int i=hd[u],v=edge[i].t;i;i=edge[i].pr,v=edge[i].t){
            --in[v];
            if(in[v]==0)ts[++pt]=v,que[++qt]=v;
        }
    }
    return pt==n;
}