#include <fstream>
#include <vector>
#include <cstring>
#define NMAX 1005
using namespace std;
ifstream f("party.in");
ofstream g("party.out");
int M,N;
vector <int> G[NMAX],GT[NMAX];
int O[NMAX],Solution[NMAX],K;
bool Use[NMAX];
inline int Node(int x)
{
    if(x<0)
        return N-x;
    return x;
}
inline int Non(int x)
{
    if(x<=N)
        return x+N;
    else
        return x-N;
}
void fillGraph(int x,int y)
{
    GT[x].push_back(Non(y));
    GT[y].push_back(Non(x));
    G[Non(x)].push_back(y);
    G[Non(y)].push_back(x);
}
void Read()
{
    int i,type;
    f>>N>>M;
    for(i=1;i<=M;i++)
    {
        int x,y;
        f>>x>>y>>type;
        if(type==1)
            y*=-1;
        if(type==2)
            x*=-1;
        if(type==3)
        {
            x*=-1;
            y*=-1;
        }
        x=Node(x);
        y=Node(y);
        fillGraph(x,y);
    }
}
void DFP(int Nod)
{
    Use[Nod]=1;
    for(unsigned int i=0;i<G[Nod].size();i++)
        {
            int Vecin=G[Nod][i];
            if(!Use[Vecin])
                DFP(Vecin);
        }
    O[++K]=Nod;
}

void DFM(int Nod)
{
    Use[Nod]=1;
    if(Solution[Nod]==1)
    {
        Solution[0]=-1;
        return;
    }
    Solution[Non(Nod)]=1;
    for(unsigned int i=0;i<GT[Nod].size();i++)
        {
            int Vecin=GT[Nod][i];
            if(!Use[Vecin])
                DFM(Vecin);
        }
}

void Kosaraju()
{
    for(int i=1;i<=N*2;i++)
        {
            if(!Use[i])
                DFP(i);
        }
    memset(Use,0,sizeof(Use));
    for(int i=K;i>=1;i--)
        {
            if(!Use[O[i]] && !Use[Non(O[i])])
                DFM(O[i]);
        }
}
void Print()
{
    int i;
    int result=0;
    if(Solution[0]==-1)
    {
        g<<0<<"\n";
        return;
    }
    for(i=1;i<=N;i++)
        if(Solution[i]==1)
            result++;
    g<<result<<"\n";
    for(int i=1;i<=N;i++)
        if(Solution[i]==1)
            g<<i<<"\n";
}
int main()
{
    Read();
    Kosaraju();
    Print();
    return 0;
}