#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <fstream>
using namespace std;
 
const string file = "party";
 
const string infile = file + ".in";
const string outfile = file + ".out";


vector<int> values;
vector<vector<int> > G;

int N;
int M;

inline int non(int x)
{
	return x <= N ? x + N : x - N;
}




vector<int> ind;
vector<int> lowlink;
vector<bool> assined;
stack<int> stiva;
vector<vector<int> > ctc;

void Tarjan(int x, int& c)
{
	ind[x] = lowlink[x] = ++c;
	stiva.push(x);

	for(vector<int>::iterator itr = G[x].begin();
		itr != G[x].end();
		itr++)
	{
		if(ind[*itr] == 0)
		{
			Tarjan(*itr, c);
			lowlink[x] = min(lowlink[x], lowlink[*itr]);
		}
		else if(assined[*itr] == false)
		{
			lowlink[x] = min(lowlink[x], lowlink[*itr]);
		}
	}


	if(ind[x] == lowlink[x])
	{
		vector<int> newCtc;
		int nod = -1;
		while(nod != x)
		{
			nod = stiva.top();
			stiva.pop();
			assined[nod] = true;
			newCtc.push_back(nod);
		}
		ctc.push_back(newCtc);
	}


}

int main()
{
	fstream fin(infile.c_str(), ios::in);

	fin >> N >> M;
	G.resize(2*N + 1);

	for(int i = 0; i < M; i++)
	{
		int x, y, z;

		fin >> x >> y >> z;
		if( 2 & z) x = non(x);
		if( 1 & z) y = non(y);

		G[non(x)].push_back(y);
		G[non(y)].push_back(x);

	}

	fin.close();
	int c = 0;
	ind.resize(2* N + 1);
	lowlink.resize(2 * N + 1);
	assined.resize(2 * N + 1);

	for(int i = 1; i <= 2*N; i++)
	{
		if(ind[i] == 0)
		{
			Tarjan(i, c);
		}
	}


	values.resize(N + 1, -1);
	int size = 0;

	for(vector<vector<int> >::reverse_iterator itr = ctc.rbegin();
		itr != ctc.rend();
		itr++)
	{
		for(vector<int>::iterator itr2 = itr->begin();
			itr2 != itr->end();
			itr2++)
		{
			int value = *itr2 <= N ? 0 : 1;
			int nod = *itr2 <= N ? *itr2 : non(*itr2);
			
			if(values[nod] == -1)
			{
				values[nod] = value;
				if(value == 1) size++;
			}
			else
			{
				break;
			}

		}
	}




	fstream fout(outfile.c_str(), ios::out);
	fout << size << "\n";
	for(int i = 1; i <= N; i++)
	{
		if(values[i] == 1) fout << i << "\n";
		//fout << values[i] << "\n";
	}


	fout.close();

}