CAPCITY - Capital City

# include <iostream>
# include <vector>
# include <algorithm>
# define ll long long
  using namespace std;
  ll index, kol_compo;
  ll color[100100], low_link[100100], id[100100], in_srr[100100], pred[100100];
  vector< ll > srr, tops;
  vector< ll > Gr[100100], new_Gr[100100], from[100100], compo[100100];
  void way(ll v)
  {
      color[v] = 1;
      for(ll x : Gr[v]){
        if(color[x] == 0) way(x);
      }
      for(ll x : from[v]){
        if(color[x] == 0) way(x);
      }
  }
  void Tarjan(ll v)
  {
      color[v] = 1;
      low_link[v] = index;
      id[v] = index;
      index++;
      srr.push_back(v);
      in_srr[v] = 1;
      for(ll x : Gr[v]){
        if(color[x] == 0){
            Tarjan(x);
            low_link[v] = min(low_link[v], low_link[x]);
        }
        else if(in_srr[x] == 1){
            low_link[v] = min(low_link[v], id[x]);
        }
      }
      if(id[v] == low_link[v]){
        kol_compo++;
        int x;
        do {
            x = srr.back();
            srr.pop_back();
            in_srr[x] = 0;
            compo[kol_compo].push_back(x);
            pred[x] = kol_compo;
        } while(x != v);
      }
  }
  void top_sort(ll v)
  {
      color[v] = 1;
      for(ll x : new_Gr[v]){
        if(color[x] == 0) top_sort(x);
      }
      tops.push_back(v);
  }
  int main()
  {
      ios_base::sync_with_stdio(0);
      cin.tie(NULL);
      cout.tie(NULL);
      ll n, m, a, b, i;
      cin >> n >> m;
      for(i = 1; i <= m; i++){
        cin >> a >> b;
        Gr[a].push_back(b);
        from[b].push_back(a);
      }

      /// Step 1 : Chek all nodes - in one component unorder Graph
      fill(color + 1, color + 1 + n, 0);
      way(1);
      for(i = 1; i <= n; i++){
        if(color[i] == 0){
            cout << "0";
            return 0;
        }
      }

      /// Step 2 : Find all strong components
      /// Step 3 : Fill pred[ ] where pred[x] = y, mean x - in strong component number y
      index = 0;
      fill(color + 1, color + 1 + n, 0);
      for(i = 1; i <= n; i++){
        if(color[i] == 0) Tarjan(i);
      }

      /// Step 4 : Make new Graph
      for(i = 1; i <= kol_compo; i++){
        for(ll v : compo[i]){
            for(ll x : Gr[v]){
                if(pred[x] != i) new_Gr[i].push_back(pred[x]);
            }
        }
      }

      /// Step 5 : Make nodes in new_Graph topological sort
      fill(color + 1, color + 1 + n, 0);
      for(i = 1; i <= n; i++){
        if(color[i] == 0) top_sort(i);
      }
      ///reverse(tops.begin(), tops.end());

      /// Step 6 : sort Answer is first node in tops
      sort(compo[tops[0]].begin(), compo[tops[0]].end());

      /// Step 7 : Answer is first node in tops
      cout << compo[tops[0]].size() << '\n';
      for(ll v : compo[tops[0]]){
        cout << v << " ";
      }

      return 0;
  }