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#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
#include <map>
#include <string>
#include <sstream>
#include <cstdlib>
#include <ctime>
#include <iterator>
#include <stack>
#include <queue>

using namespace std;
typedef pair<int, int> P;

// graph has outgoing edges, dual has incoming edges
map<int, pair<set<int>, set<int> > > graph; // node, edges in graph, edges in dual graph
map<int, set<int> > sccs; // scc leader number, nodes in it
map<int, bool> vr;
map<int, bool> v;
priority_queue<P, vector<P>, less<P> > fs; //first f, second node
priority_queue<P, vector<P>, less<P> > scs; //first size, second leader 
int s;
int t = 0;

void DFSr(int node) {
    if(vr[node])
	    return;
    vr[node] = true;
    for(set<int>::iterator itn = graph[node].second.begin(); itn != graph[node].second.end(); ++itn) {
//	    cout << "Internal DFS " << *itn << endl;
	    if(!vr[*itn])
		    DFSr(*itn);
    }
    ++t;
    fs.push(make_pair(t, node));
//    cout << "Finished visiting node " << node << " t " << t << endl;
}

void DFS(int node) {
    if(v[node])
	    return;
//    cout << "Marking node " << node << " as a follower of " << s << endl;
    v[node] = true;
    sccs[s].insert(node);
    for(set<int>::iterator itn = graph[node].first.begin(); itn != graph[node].first.end(); ++itn) {
	    if(!v[*itn])
		    DFS(*itn);
    }
//    cout << "Finished marking node " << node << " leader " << s << endl;
}

int main()
{
    string line;
    std::ios_base::sync_with_stdio (false);
    getline(cin, line); // skip redundant data

    while (getline(cin, line)) {
	istringstream is(line);
	vector<int> edge = vector<int>(istream_iterator<int>(is), istream_iterator<int>());
//	cout << "edge from: " << edge[0] << " to : " << edge[1] << endl;
	if(graph.find(edge[0]) != graph.end()) {
		graph[edge[0]].first.insert(edge[1]);
	} else {
		graph[edge[0]] = make_pair(set<int>(), set<int>());
		graph[edge[0]].first.insert(edge[1]);
		vr[edge[0]] = false;
		v[edge[0]] = false;
	}
	if(graph.find(edge[1]) != graph.end()) {
		graph[edge[1]].second.insert(edge[0]);
	} else {
		graph[edge[1]] = make_pair(set<int>(), set<int>());
		graph[edge[1]].second.insert(edge[0]);
		vr[edge[1]] = false;
		v[edge[1]] = false;
	}
    }

    int t = 0;

    for(map<int, pair<set<int>, set<int> > >::iterator it = graph.begin(); it != graph.end(); ++it) {
	    int node = it->first;
//	    cout << "Going to node " << it->first << endl;
//	    cout << "Straight edges to ";
//	    for(set<int>::iterator itn = graph[node].first.begin(); itn != graph[node].first.end(); ++itn) {
//		    cout << *itn << " ";
//	    }
//	    cout << endl;
//	    cout << "Reverse edges to ";
//	    for(set<int>::iterator itn = graph[node].second.begin(); itn != graph[node].second.end(); ++itn) {
//		    cout << *itn << " ";
//	    }
//	    cout << endl;
		
	    DFSr(it->first);
    }

//    cout << "Phase two" << endl;
//    cout << "fs size " << fs.size() << endl;
    while(!fs.empty()) {
//	    cout << "current fs " << fs.top().first << "/" << fs.top().second << endl;
	    s = fs.top().second;
	    fs.pop();
	    // second DFS on normal graph
	    if(!v[s]) {
//		    cout << "Visiting leader node " << s << endl;
		    // DFS it!
		    sccs[s] = set<int>();
		    DFS(s);
	    }
    }

    for(map<int, set<int> >::iterator it = sccs.begin(); it != sccs.end(); ++it) {
//	    cout << "SCCS with leader: " << it->first << " containing: ";
//	    for(set<int>::iterator itn = it->second.begin(); itn != it->second.end(); ++itn) {
//		    cout << *itn << " ";
//	    }
//	    cout << endl;
	    scs.push(make_pair(it->second.size(), it->first));
    }
  
    int big_count = 0;
    int bl = -1; // big_leader
    while(!scs.empty()) {
//	    cout << "SCS with leader: " << scs.top().second << " count " << scs.top().first << endl;
	    if (scs.top().first > 1) {
		bl = scs.top().second;
		++big_count;
	    }
	    scs.pop();
    }
    
    if (big_count != 1) {
	cout << "NIE" << endl;
    } else {
	// filter the graph to contain only the ones in the SCS
	map<int, pair<set<int>, set<int> > > fgraph;
	int maxout = -1;
	int maxin = -1;
	for(set<int>::iterator itn = sccs[bl].begin(); itn != sccs[bl].end(); ++itn) {
//		cout << *itn << " ";
       		set<int> outs;
		set<int> ins;

		int v = *itn;

    		std::set_intersection(graph[v].first.begin(), graph[v].first.end(),
                          sccs[bl].begin(), sccs[bl].end(),
                          std::inserter(outs, outs.begin()));

    		std::set_intersection(graph[v].second.begin(), graph[v].second.end(),
                          sccs[bl].begin(), sccs[bl].end(),
                          std::inserter(ins, ins.begin()));

		if (maxout < outs.size()) {
			maxout = outs.size();
		}

		if (maxin < ins.size()) {
			maxin = ins.size();
		}
		fgraph[v] = make_pair(outs, ins);
 	}
//	cout << endl;

	// calculate the degrees, if out is always 1 then all in cycle
	if (maxout == 1) {
//		cout << "FINAL" << endl;
		for(set<int>::iterator itn = sccs[bl].begin(); itn != sccs[bl].end(); ++itn) {
			cout << *itn << " ";
 		}
		cout << endl;
		return 0;
	}

	// otherwise start from leader and run a dfs (might be simple next next next while not again leader)
	// and mark from the one that has in > 1 to the one that has out > 1
	int lastin = -1;
	int firstin = -1;
	int lastout = -1;
	int firstout = -1;
	vector<int> mc; //main cycle
	int v = bl;
	do {
//		cout << "mc node: " << v << endl;
		if ((firstout == -1) && (fgraph[v].first.size() > 1)) {
			firstout = v;
		}
		if (fgraph[v].first.size() > 1) {
			lastout = v;
		}
    		if ((firstin == -1) && (fgraph[v].second.size() > 1)) {
			firstin = v;
		}
		if (fgraph[v].second.size() > 1) {
			lastin = v;
		}
		mc.push_back(v);
		v = *(fgraph[v].first.begin());
	} while (v != bl);
//	cout << "DEGz" << endl;
//	cout << "fi " << firstin << " li " << lastin << " fo " << firstout << " lo " << lastout << endl;

	if(lastin == -1)
		lastin = bl;
	if(firstout == -1);
		firstout = mc[mc.size() - 1];	
	// extend for case li > fo
	for (int el : mc) {
		mc.push_back(el);
	}

	set<int> result;
	int i = 0;
	while (mc[i] != lastin)
		++i;
	result.insert(mc[i]);
	while (mc[i] != firstout) {
		++i;
		result.insert(mc[i]);
	}
	cout << result.size() << endl;
	for (int vres : result) {
		cout << vres << " ";
	}
	cout << endl;
    }
    
    return 0;
}