#include <stdio.h>
 
#define maxn 10000
 
int os[maxn+1],van_szulo[maxn+1],van_gyerek[maxn+1],szulo[maxn+1][2];
int n;
 
void fun(int k){
 
   if(!van_szulo[k])return;
   int i,u;
 
   for(i=0;i<2;i++){
      u=szulo[k][i];
      if(!os[u]){os[u]=1;fun(u);}
   }
}
 
void Beolvas(){
   int m,p,q1,q2;
   scanf("%d%d",&n,&m);
   for(int i=1;i<=n;i++){van_szulo[i]=0;van_gyerek[i]=0;}
   for (int i=0;i<m;i++){
      scanf("%d%d%d",&p,&q1,&q2);
      szulo[p][0]=q1;
      szulo[p][1]=q2;
      van_szulo[p]=1;
      van_gyerek[q1]=1;
      van_gyerek[q2]=1;
   }
}
 
int main(void){
 
   Beolvas();
   int cnt,i,u,kozos_os[maxn+1];
 
   for(u=1;u<=n;u++)kozos_os[u]=1;
 
   for(i=1;i<=n;i++)if(!van_gyerek[i]){
      for(u=1;u<=n;u++)os[u]=0;
      fun(i);
      for(u=1;u<=n;u++)kozos_os[u]&=os[u];
   }
 
   cnt=0;
   for(u=1;u<=n;u++)cnt+=kozos_os[u];
 
   printf("%d\n",cnt);
   cnt=0;for(u=1;u<=n;u++)if(kozos_os[u]){if(cnt)printf(" ");cnt++;printf("%d",u);}
   if(cnt)printf("\n");
 
   return 0;
}
 

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