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// tested by Hightail: https://github.com/dj3500/hightail
#include <iostream>
#include <cstdio>
#include <string>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <cmath>
#include <algorithm>
#include <sstream>
#include <stack>
#include <cstring>
#include <iomanip>
#include <ctime>
#include <cassert>
using namespace std;
#define pb push_back
#define INF 1001001001
#define FOR(i,n) for(int (i)=0;(i)<(n);++(i))
#define FORI(i,n) for(int (i)=1;(i)<=(n);++(i))
#define mp make_pair
#define pii pair<int,int>
#define ll long long
#define vi vector<int>
#define SZ(x) ((int)((x).size()))
#define fi first
#define se second
#define wez(n) int (n); scanf("%d",&(n));
#define wez2(n,m) int (n),(m); scanf("%d %d",&(n),&(m));
#define wez3(n,m,k) int (n),(m),(k); scanf("%d %d %d",&(n),&(m),&(k));
inline void pisz(int n) { printf("%d\n",n); }
template<typename T,typename TT> ostream& operator<<(ostream &s,pair<T,TT> t) {return s<<"("<<t.first<<","<<t.second<<")";}
template<typename T> ostream& operator<<(ostream &s,vector<T> t){FOR(i,SZ(t))s<<t[i]<<" ";return s; }
#define DBG(vari) cout<<"["<<__LINE__<<"] "<<#vari<<" = "<<(vari)<<endl;
#define ALL(t) t.begin(),t.end()
#define FOREACH(i,t) for (__typeof(t.begin()) i=t.begin(); i!=t.end(); i++)
#define TESTS wez(testow)while(testow--)
#define REP(i,a,b) for(int (i)=(a);(i)<=(b);++i)
#define REPD(i,a,b) for(int (i)=(a); (i)>=(b);--i)
#define REMAX(a,b) (a)=max((a),(b));
#define REMIN(a,b) (a)=min((a),(b));
#define IOS ios_base::sync_with_stdio(0);

const int N = 500007;
int n,       // input
ind[N],    // temp
lowlink[N],  // temp
onstack[N],  // temp
last,        // temp
n2,          // output
t[N];        // output
vi adj[N],   // input
st;          // temp

void go (int v) {
   ind[v] = lowlink[v] = ++last;
   st.pb(v);
   onstack[v] = 1;
   FOREACH(w,adj[v]) {
      if (!ind[*w]) {
         go(*w);
         lowlink[v] = min(lowlink[v], lowlink[*w]);
      } else if (onstack[*w]) {
         lowlink[v] = min(lowlink[v], lowlink[*w]);
      }
   }
   if (lowlink[v] == ind[v]) { // v is a root node
      ++n2;
      for (int w = -1; w != v; ) {
         w = st.back();
         st.pop_back();
         onstack[w] = 0;
         t[w] = n2;
      }
   }
}

void scc() {
   last = n2 = 0;
   FORI(i,n) ind[i] = onstack[i] = 0;
   FORI(i,n) if (!ind[i]) go(i);
   FORI(i,n) t[i] = n2 + 1 - t[i]; // zeby byl zwykly porzadek topologiczny
}

int sccSize[N];

vi postorder;
int post[N];
int high[N];
int current = 0;

void dfs (int v) {
   post[v] = 1;
   for (int w : adj[v]) if (post[w] == 0) dfs(w);
   post[v] = high[v] = ++current;
   postorder.pb(v);
}

int main () {
   scanf("%d", &n);
   TESTS {
      wez2(a,b);
      adj[a].pb(b);
   }

   scc();
   FORI(i,n) sccSize[t[i]]++;
   int moreThanOne = 0, anySuch = -1;
   FORI(c,n2) if (sccSize[c] > 1) {
      ++moreThanOne;
      anySuch = c;
   }
   if (moreThanOne == 0) {
      printf("NIE");
   } else if (moreThanOne >= 2) {
      printf("0");
   } else {
      int root = -1;
      FORI(i,n) {
         if (t[i] != anySuch) {
            adj[i].clear(); // chyba nie trzeba
         } else {
            root = i;
            adj[i].erase(remove_if(ALL(adj[i]), [anySuch](int v){return t[v] != anySuch;}), adj[i].end());
         }
      }

      // algorytm Tarjana na robienie tego zadania
      int lowest = INF;
      dfs(root);
      vi feedback; // stos
      for (int v : postorder) {
         for (int w : adj[v]) {
            REMAX(high[v], high[w]);
            if (post[w] > post[v]) {
               REMIN(lowest, post[w]);
               feedback.clear();
            } else if (post[w] < post[v] && post[v] <= high[w]) {
               while (!feedback.empty() && post[feedback.back()] > post[w]) {
                  feedback.pop_back();
               }
            }
         }
         if (post[v] <= lowest) feedback.pb(v);
      }
      sort(ALL(feedback));
      pisz(SZ(feedback));
      for (int v : feedback) printf("%d ", v);
   }
}