#include using namespace std; using ll =long long; #define all(v) v.begin(),v.end() #define rep(i,a,b) for(int i=a;i=b;i--) ll INF=2e18; vector>> vec; vector del; vector this_sec; vector check; vector check_edge; ll dfs(ll now) { if(this_sec[now]) { return now; } if(check[now]) return -1; this_sec[now]=true; for(auto x:vec[now]) { if(del[x.second]||check_edge[x.second]) continue; ll k=dfs(x.first); if(k>=0) { del[x.second]=true; if(k!=now) { this_sec[now]=false; return k; } } else check_edge[x.second]=true; } check[now]=true; this_sec[now]=false; return -1; } int main() { ios::sync_with_stdio(false); cin.tie(0); ll N,M;cin>>N>>M; vec=vector>> (N,vector> (0)); del=vector (M); check=vector (N); check_edge=vector (N); this_sec=vector (N); for(ll i=0;i>U>>V; U--;V--; vec[U].push_back(make_pair(V,i)); } for(ll i=0;i> ans(0); for(ll i=0;i