#include <iostream>
#include <algorithm>
#include <cstdio>
#include <vector>

using namespace std;

const int N=200000+7;
int n,m,top,o[N],tip[N],cur;
bool one[N];
bool vis[N];
vector<int> g[N],ginv[N];

void dfs1(int a) {
  vis[a]=1;
  for (auto &b:g[a]) {
    if (vis[b]==0) {
      dfs1(b);
    }
  }
  o[++top]=a;
}

void dfs2(int a) {
  vis[a]=1;
  tip[a]=cur;
  for (auto &b:ginv[a]) {
    if (vis[b]==0) {
      dfs2(b);
    }
  }
}

signed main() {
  freopen ("party.in","r",stdin);
  freopen ("party.out","w",stdout);

  scanf("%d%d",&n,&m);

  for (int i=1;i<=m;i++) {
    int x,y,t;
    scanf("%d%d%d",&x,&y,&t);
    if (t==0) {
      g[x+n].push_back(y);
      g[y+n].push_back(x);
    }
    if (t==1) {
      g[x+n].push_back(y+n);
      //g[y].push_back(x);
    }
    if (t==2) {
      g[x].push_back(y);
      //g[y+n].push_back(x+n);
    }
    if (t==3) {
      g[x].push_back(y+n);
      g[y].push_back(x+n);
    }

  }

  for (int i=1;i<=2*n;i++) {
    for (auto &j : g[i]) {
      ginv[j].push_back(i);
    }
  }

  for (int i=1;i<=2*n;i++) {
    if (vis[i]==0) {
      dfs1(i);
    }
  }
  for (int i=1;i<=2*n;i++) {
    vis[i]=0;
  }
  for (int i=2*n;i>=1;i--) {
    int node=o[i];
    if (vis[node]==0) {
      cur++;
      dfs2(node);
    }
  }
  int cnt=0;
  for (int i=1;i<=n;i++) {
    cnt+=(tip[i]>tip[i+n]);
  }
  printf("%d\n",cnt);
  for (int i=1;i<=n;i++) {
    if (tip[i]>tip[i+n]) {
      printf("%d\n",i);
    }
  }
  return 0;
}