#include <fstream>
#include <vector>
#include <bitset>
#include <stack>

std::ifstream fin("party.in");
std::ofstream fout("party.out");

const int NMAX = 500;

std::vector<int> g[NMAX], rg[NMAX];
std::bitset<NMAX> used, ans;
std::stack<int> topo;
bool not_ok;
int n, m, x, y, c;

inline int neg(int x)
{
	if (x <= n)
		return x + n;
	return x - n;
}

void DFS1(int node)
{
	used[node] = 1;
	for (auto& i : g[node])
		if (used[i] == 0)
			DFS1(i);
	topo.push(node);
}

void DFS2(int node)
{
	if (ans[node] == 1)
		not_ok = true;
	used[node] = 1;
	ans[neg(node)] = 1;
	for (auto& i : rg[node])
		if (used[i] == 0)
			DFS2(i);
}

void poz()
{
	if (c == 1)
		y += n;
	else if (c == 2)
		x += n;
	else if (c == 3)
	{
		x += n;
		y += n;
	}
}

int main()
{
	fin >> n >> m;
	for (int i = 1; i <= m; ++i)
	{
		fin >> x >> y >> c;
		poz();
		int negx = neg(x), negy = neg(y);
		g[negx].push_back(y);
		g[negy].push_back(x);
		rg[x].push_back(negy);
		rg[y].push_back(negx);
	}

	for (int i = 1; i <= 2 * n; ++i)
		if (used[i] == 0)
			DFS1(i);

	used.reset();

	while (!topo.empty())
	{
		x = topo.top();
		topo.pop();
		if (used[x] == 0 && used[neg(x)] == 0)
			DFS2(x);
	}

	int cnt(0);
	for (int i = 1; i <= n; ++i)
		if (ans[i])
			cnt++;
	fout << cnt << "\n";
	for (int i = 1; i <= n; ++i)
		if (ans[i])
			fout << i << "\n";


	return 0;
}