#include <cstdio>
#define DM 2005

bool ok=true,viz[DM];
int sol[DM],ord[DM],n,m,nr;

struct nod {
	int x;
	nod *urm;
} *g[DM],*gt[DM];

inline int non (int a) {
	return (a>n)?a-n:a+n;
}

void adaugare(int x, int y, bool z) {
	nod *p;
	p=new nod;
	p->x=y;
	if(z) {
		p->urm=g[x];
		g[x]=p;
	}else {
		p->urm=gt[x];
		gt[x]=p;
	}
}

void dfs(int sursa) {
	nod *p;
	if(viz[sursa]) return;
	viz[sursa]=true;
	for(p=g[sursa];p!=NULL; p=p->urm)
		if(!viz[p->x]) dfs(p->x);
	ord[++nr]=sursa;
}

void dfs_2(int sursa) {
	nod *p;
	if(!viz[sursa]) return;
	viz[sursa]=false;
	sol[non(sursa)]=1;
	for(p=gt[sursa];p!=NULL; p=p->urm)
		if(viz[p->x]) dfs_2(p->x);
}

int main()
{
	int x,y,z,i;
	freopen("party.in","r",stdin);
	freopen("party.out","w",stdout);
	scanf("%d %d",&n,&m);
	for(i=1; i<=m; ++i) {
		scanf("%d %d %d",&x,&y,&z);
		if(z==1) y+=n;
		else if(z==2) x+=n;
		else if(z==3) y+=n,x+=n;
		adaugare(non(x),y,true);
		adaugare(non(y),x,true);
		adaugare(y,non(x),false);
		adaugare(x,non(y),false);
	}
	for(i=1; i<=n+n; ++i) if(!viz[i]) dfs(i);
	for(i=1; i<=n+n; ++i) if(viz[ord[i]] && viz[non(ord[i])]) dfs_2(ord[i]);
	nr=0;
	for(i=1; i<=n; ++i) if(sol[i]) ++nr;
	printf("%d\n",nr);
	for(i=1; i<=n; ++i) if(sol[i]) printf("%d\n",i);
	return 0;
}