#include <iostream>
#include <vector>
#include <list>
using namespace std;

class Graph {
  public:
    Graph(int V): vert(V) {}~Graph() {}
  void addEdge(int u, int v) { adj[u].push_back(v); }
  const list<int> & edges(int u) const { return adj[u]; }
  bool cycle(vector < int > & path) const{// a(v) < a(u) < t(u) < t(v) // u->v
	  dfs(p,A,T);
	  for(int w:A){
	  	for(int k:A){
	  		if (A[k]<A[w]<T[w]<T[k]){
			  for(int l:p){
			  	if(p[l]==w)
			  }
			  return true;
			  }
		  }

	  }
  }

  private:
  	vector<list<int>> adj;
    int vert;
	enum state {UNVISITED, SEEN, VISITED};
    vector<int> p,A,T;
  void dfs_help(int u, int & time,vector < int > & p,
      vector < int > & A, vector < int > & T,
      vector < state > & status) {
    status[u] = SEEN;
    A[u] = ++time;
    for (int v: edges(u))
      if (status[v] == UNVISITED) {
        p[v] = u;
        dfs_help(v, time, p, A, T, status);
      }
    status[u] = VISITED;
    T[u] = ++time;
  }

  void dfs(vector < int > & p,
    vector < int > & A, vector < int > & T) {
    int N = vert;
    vector < state > status(N);
    for (int u = 0; u < N; ++u) {
      p[u] = -1;
      status[u] = UNVISITED;
    }
    int time = 0;
    for (int u = 0; u < N; ++u)
      if (status[u] == UNVISITED)
        dfs_help(u, time, p, A, T, status);
  }

};

int main() {
  int V, E;
  cin >> V >> E;
  Graph g(V);
  for (int i = 0; i < E; ++i) {
    int u, v;
    cin >> u >> v;
    g.addEdge(u, v);
  }
  vector < int > path;
  bool c = g.cycle(path);
  if (c) {
    cout << "CYCLE:";
    for (int i = 0; i < path.size(); ++i)
      cout << path[i] << (i == path.size() - 1 ? "\n" : "");
  } else {
    cout << "NO CYCLE" << endl;
  }
}