#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll=long long;
using Graph=vector<vector<pair<int,int>>>;
#define MAX 100
#define MOD 1000000007
#define INF 1000000000000000000

int main(){
  int N,M;
  cin>>N>>M;
  Graph G(N);
  vector<int> a(M),b(M);
  vector<char> c(M);
  for(int i=0;i<M;i++){
    cin>>a[i]>>b[i]>>c[i];
    a[i]--;b[i]--;
    G[a[i]].push_back(make_pair(b[i],i));
    G[b[i]].push_back(make_pair(a[i],i));
  }
  bool flag=false;
  for(int i=1;i<M;i++){
    if(c[i]!=c[0]){
      flag=true;
    }
  }
  if(flag==false){
    cout<<-1<<endl;
    return 0;
  }

  int v=0;
  vector<int> edges;
  edges.push_back(G[v][0].second);
  v=G[v][0].first;
  vector<int> dist(N,N+5);
  dist[v]=0;
  queue<int> q;
  q.push(v);
  while(!q.empty()){
    int v=q.front();
    q.pop();
    for(auto p:G[v]){
      int nv=p.first;
      int e=p.second;
      if(dist[nv]>dist[v]+1){
        dist[nv]=dist[v]+1;
        q.push(nv);
      }
    }
  }

  int k;
  for(int i=0;i<M;i++){
    if(c[i]!=c[edges[0]]){
      k=i;
      break;
    }
  }

  vector<int> edges2;
  if(dist[a[k]]<dist[b[k]]){
    v=b[k];
    edges2.push_back(k);
    v=a[k];
  }else{
    v=a[k];
    edges2.push_back(k);
    v=b[k];
  }
  while(dist[v]!=0){
    for(auto p:G[v]){
      int nv=p.first;
      int e=p.second;
      if(dist[nv]==dist[v]-1){
        v=nv;
        edges2.push_back(e);
        break;
      }
    }
  }
  for(int i=edges2.size()-1;i>=0;i--){
    edges.push_back(edges2[i]);
  }
  if(dist[a[k]]<dist[b[k]]){
    v=b[k];
  }else{
    v=a[k];
  }
  for(int i=0;i<N;i++){
    dist[i]=N+5;
  }
  dist[v]=0;
  q.push(v);
  while(!q.empty()){
    int v=q.front();
    q.pop();
    for(auto p:G[v]){
      int nv=p.first;
      int e=p.second;
      if(dist[nv]>dist[v]+1){
        dist[nv]=dist[v]+1;
        q.push(nv);
      }
    }
  }
  vector<int> edges3;
  v=N-1;
  while(dist[v]!=0){
    for(auto p:G[v]){
      int nv=p.first;
      int e=p.second;
      if(dist[nv]==dist[v]-1){
        v=nv;
        edges3.push_back(e);
        break;
      }
    }
  }
  for(int i=edges3.size()-1;i>=0;i--){
    edges.push_back(edges3[i]);
  }

  string S="";
  for(int i=0;i<edges.size();i++){
    S+=c[edges[i]];
  }
  bool kaibun=true;
  for(int i=0;i<edges.size()/2;i++){
    if(S[i]!=S[edges.size()-1-i]){
      kaibun=false;
    }
  }
  if(kaibun==true){
    int e=G[N-1][0].second;
    edges.push_back(e);
    edges.push_back(e);
  }

  cout<<edges.size()<<endl;
  for(int i=0;i<edges.size();i++){
    cout<<edges[i]+1<<" ";
  }
  cout<<endl;
}