1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
//na podstawie ksiazki "algorytmika praktyczna"
#include <cstdio>
#include <iostream>
#include <algorithm>
#include <string>
#include <vector>

using namespace std;

typedef vector<int> VI;
typedef long long LL;

int ss[500000];
int cykle[500000];
int cyk;
int n, m, b, e, k;
bool f, f2;

#define FOR(x, b, e) for(int x = b; x <= (e); ++x)
#define FORD(x, b, e) for(int x = b; x >= (e); --x)
#define REP(x, n) for(int x = 0; x < (n); ++x)
#define VAR(v, n) __typeof(n) v = (n)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(x) ((int)(x).size())
#define FOREACH(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define PB push_back
#define ST first
#define ND second
#include <list>
template<class V, class E> struct Graph {
	struct Ed : E {
		int v; 
		Ed(E p, int w) : E(p), v(w) {}
	};
    
	struct Ve : V, vector<Ed> {};
	vector<Ve> g;
	Graph(int n = 0) : g(n) {}
    
	void EdgeD(int b, int e, E d = E()) {
        g[b].PB(Ed(d, e));
    }

    void Write() {
        REP(x, SIZE(g)) {
            cout << x << ":";
            FOREACH(it, g[x]) cout << " " << it->v;
            cout << endl;
        }
    }
    
  VI vis;
  VI curr;
  void SccDfs(int v, int nr, bool phase){
    curr.PB(v);
    g[v].t = 1;
	if(!phase) vis[v] = nr;
    FOREACH(it, g[v]) 
        if (g[it->v].t == -1)
            SccDfs(it->v, nr, phase);
        else if(!phase) {
            bool flag = false;
            cyk++;
            FOREACH(it2, curr) {
                if((*it2) == it->v) flag = true;
                if(flag) {
                    cykle[*it2]++;
                }
            }
        }
	if(phase) 
        vis.PB(v); 
    else 
        g[v].t = nr;
    curr.pop_back();
  }
  
  void Scc() {
    Graph<V,E> gt(SIZE(g)), *tab[]={this, &gt};
    gt.vis.resize(SIZE(g), -1); 
    vis.clear();
    
    REP(i,SIZE(g)) 
        FOREACH(it,g[i]) 
            gt.EdgeD(it->v, i);
        
    REP(i, 2){
      FOREACH(it, tab[i]->g) it->t = -1;
      int comp = 0, v;
      FORD(j, SIZE(g) - 1, 0)
        if (tab[i]->g[v = (i ? vis[j] : j)].t == -1) 
            tab[i]->SccDfs(v, comp++, 1 - i);
    }
    REP(i, SIZE(g)) g[i].t = gt.g[i].t;
    return;
  }
};
struct Ve {}; 
struct Vs {
	int t;
};
int main() {
	scanf("%d%d",&n,&m);
	Graph<Vs, Ve> g(n);
	REP(x, m) {
		scanf("%d%d",&b,&e);
        b--; e--;
		g.EdgeD(b, e);
	}
    g.Scc();
    
    
    REP(x, n) {
       ss[g.g[x].t]++; 
    }
    
    REP(x, n) {
        if(f && ss[x] > 1) f2 = true;
        if(ss[x] > 1) f = true;
    }
    
    if(!f) printf("NIE\n");
    else {
        if(f2) {
            printf("0\n\n");
        }
        else {
            REP(x, n) if(cykle[x] == cyk) k++;
            printf("%d\n", k);
            REP(x, n) if(cykle[x] == cyk) printf("%d ", x + 1);
            printf("\n");
        }
    }
	return 0;
}