#include <cstdio>
#include <vector>
#include <stack>

#define NMAX 1007
#define neg(a) (a^1)

using namespace std;
int n, m, x, y, p, viz[NMAX], sol[NMAX], ct;
vector <int> g[NMAX], gt[NMAX];
stack <int> order;
void convert(int &a)
{
    if(a < 0) a = (((0-a)<<1) | 1);
    else a = (a<<1);
}
void add(const int &a, const int &b)
{
    g[a].push_back(b);
    gt[b].push_back(a);
}
void create()
{
    if(p == 0)
    {
        add(neg(x), y);
        add(neg(y), x);
    }
    if(p == 1) add(neg(x), neg(y));
    if(p == 2) add(x, y);
    if(p == 3)
    {
        add(x, neg(y));
        add(y, neg(x));
    }
}
void dfsort(const int &nod)
{
    viz[nod] = 1;
    for(int i = g[nod].size()-1; i+1; --i)
    {
        if(!viz[g[nod][i]]) dfsort(g[nod][i]);
    }
    order.push(nod);
}
void dfsat(const int &nod)
{
    viz[nod] = 0;
    //sol[nod] = 0;
    sol[neg(nod)] = 1;
    if(nod&1) ++ct;
    for(int i = gt[nod].size()-1; i+1; --i)
    {
        if(viz[gt[nod][i]]) dfsat(gt[nod][i]);
    }
}
void sortare()
{
    int tmp;
    for(int i = 1; i<= n; ++i)
    {
        tmp = (i<<1);
        if(!viz[tmp]) dfsort(tmp);
        tmp = (tmp|1);
        if(!viz[tmp]) dfsort(tmp);
    }
}
void sat()
{
    int tmp;
    while(!order.empty())
    {
        tmp = order.top();
        order.pop();
        if(viz[tmp] && viz[neg(tmp)]) dfsat(tmp);
    }
}
int main()
{
    freopen("party.in", "r", stdin);
    freopen("party.out", "w", stdout);
    scanf("%d %d", &n, &m);
    for(int i = 1; i<= m; ++i)
    {
        scanf("%d %d %d", &x, &y, &p);
        convert(x); convert(y);
        create();
    }
    sortare();
    sat();
    printf("%d\n", ct);
    for(int i = 1; i<= n; ++i)
    {
        if(sol[(i<<1)]) printf("%d\n", i);
    }
    return 0;
}