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
136
137
138
139
140
141
142
143
144
145
146
147
148
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<iostream>
#include<cstdlib>
#include<cmath>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<bitset>
using namespace std;
typedef long long ll;
typedef double db;
const db pi=acos(-1);
void gn(int &x){
    int sg=1;char c;while(((c=getchar())<'0'||c>'9')&&c!='-');
    if(c=='-')sg=-1,x=0;else x=c-'0';
    while((c=getchar())>='0'&&c<='9')x=x*10+c-'0';
    x*=sg;
}
void gn(ll &x){
    int sg=1;char c;while(((c=getchar())<'0'||c>'9')&&c!='-');
    if(c=='-')sg=-1,x=0;else x=c-'0';
    while((c=getchar())>='0'&&c<='9')x=x*10+c-'0';
    x*=sg;
}
int gcd(int a,int b){return b?gcd(b,a%b):a;}
int n,m;
//#define N 500005
#define N 1000005
#define M 1000005
struct edge{
	int v,next;
}e[M+N];int g[N*2];int etot=0;
void ae(int u,int v){
	e[etot].v=v;e[etot].next=g[u];g[u]=etot++;
}
int vis[N*2],ine[N*2],pre[N*2];
int cyfound=0;

int cy[N*2],cylen=0;
int oncy[N+M];
void fincy(int u){
	vis[u]=1;
	for (int i=g[u];~i;i=e[i].next)
		if(vis[e[i].v]==0){
			ine[e[i].v]=i;
			pre[e[i].v]=u;
			fincy(e[i].v);
			if(cyfound)return;
		}else if(vis[e[i].v]==1){
			cyfound=1;
			int x=u;
			while(x!=e[i].v){
				cy[++cylen]=x;
				oncy[ine[x]]=1;
				x=pre[x];
			}
			cy[++cylen]=e[i].v;
			oncy[ine[e[i].v]=i]=1;
			for (int i=1;i<cylen-i+1;i++)swap(cy[i],cy[cylen-i+1]);
			return;
		}
	vis[u]=2;
}
int deg[N*2]={0};
int qu[N*2],p,q;
int topo(){
	for (int u=1;u<=2*n;u++)
		for (int i=g[u];~i;i=e[i].next)if(!oncy[i])deg[e[i].v]++;
	p=q=0;
	for (int u=1;u<=2*n;u++)if(deg[u]==0)qu[q++]=u;
	while(p!=q){
		int u=qu[p++];
		for (int i=g[u];~i;i=e[i].next)if(!oncy[i]){
			deg[e[i].v]--;
			if(deg[e[i].v]==0)qu[q++]=e[i].v;
		}
	}
	if(q!=2*n)return 0;
	return 1;
}
int lef[N*2]={0},rig[N*2]={0};
int off[N+M]={0};
int main()
{
	/*freopen("1.in","r",stdin);
	freopen("jc.out","w",stdout);*/
	gn(n);gn(m);
	memset(g,-1,sizeof(g));
	for (int i=1;i<=n;i++)ae(i,i+n);
	while(m--){
		int x,y;

		gn(x);gn(y);
		ae(x+n,y);
	}
	for (int u=1;u<=2*n;u++)if(!vis[u]){
		fincy(u);
		if(cyfound)break;
	}
	if(!cyfound){
		printf("NIE\n");
		return 0;
	}
	if(!topo()){
		printf("0\n\n");
		return 0;
	}
	for (int i=1;i<=cylen;i++)lef[cy[i]]=rig[cy[i]]=i;

	for (int j=2*n-1;j>=0;j--){
		int u=qu[j];
		if(!lef[u])lef[u]=1000000000;
		for (int i=g[u];~i;i=e[i].next)if(!oncy[i])lef[u]=min(lef[u],lef[e[i].v]);
	}
	for (int j=0;j<2*n;j++){
		int u=qu[j];
		for (int i=g[u];~i;i=e[i].next)if(!oncy[i])rig[e[i].v]=max(rig[e[i].v],rig[u]);
	}
	int r=cylen+1,l=0;
	for (int i=cylen;i>=1;i--)if(lef[cy[i]]<i)r=i;
	for (int i=1;i<=cylen;i++)if(rig[cy[i]]>i)l=i;
	if(l!=0){
		for (int i=1;i<=l;i++)off[ine[cy[i]]]=1;
		for (int i=r+1;i<=cylen;i++)off[ine[cy[i]]]=1;
	}
	for (int i=1;i<=2*n;i++)rig[i]=0;
	for (int i=1;i<=cylen;i++)rig[cy[i]]=i;
	for (int j=2*n-1;j>=0;j--){
		int u=qu[j];
		for (int i=g[u];~i;i=e[i].next)if(!oncy[i])rig[u]=max(rig[u],rig[e[i].v]);
	}
	int far=0;
	for (int i=1;i<=cylen;i++)if(rig[cy[i]]>far){
		for (int j=max(i,far)+1;j<=rig[cy[i]];j++)off[ine[cy[j]]]=1;
		far=rig[cy[i]];
	}
	int cnt=0;
	for (int i=0;i<n;i++)if(oncy[i] && !off[i])cnt++;
	printf("%d\n",cnt);
	for (int i=0;i<n;i++)if(oncy[i] && !off[i]){
		printf("%d ",i+1);
	}
	printf("\n");
	return 0;
}