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

using namespace std;
using ll = long long;

#include<set>
int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int n,m;
    cin>>n>>m;
    vector<vector<pair<int,pair<char,int>>>> g(n);
    set<char> s;
    for(int i = 0;i<m;i++){
        int u,v;
        char c;
        cin>>u>>v>>c;
        u--;v--;
        s.insert(c);
        g[u].push_back({v,{c,i+1}});
        g[v].push_back({u,{c,i+1}});
    }
    if(s.size()==1){
        cout<<-1<<endl;
        return 0;
    }
    char no = g[n-1][0].second.first;
    int wu,ni;
    ni = -1;
    for(int i = 0;i<n;i++){
        for(auto itr:g[i]){
            if(itr.second.first==no) continue;
            wu = i;
            ni = itr.second.second;
            break;
        }
        if(ni!=-1) break;
    }

    vector<int> vis(n,0);
    bool fn = false;
    vector<int> que;
    auto dfs = [&](auto dfs,int ni,int to) -> void {
        vis[ni]++;
        if(ni==to){
            fn = true;
            return;
        }
        for(auto&itr:g[ni]){
            int nj = itr.first;
            if(vis[nj]) continue;
            que.push_back(itr.second.second);
            dfs(dfs,nj,to);
            if(fn) return;
            que.pop_back();
        }
    };
    dfs(dfs,0,wu);
    vector<int> ans = que;
    int cnt = ans.size();
    que.clear();
    for(int i = 0;i<n;i++) vis[i] = 0;
    int from = wu;
    ans.push_back(ni);
    int to = n - 1;
    if(cnt%2==1) to = g[n-1][0].first;
    dfs(dfs,from,to);
    for(int i:que) ans.push_back(i);
    for(int i = 0;i<cnt;i++){
        ans.push_back(g[n-1][0].second.second);
        if(to==n-1) {
            to = g[n-1][0].first;
        }else{
            to = n-1;
        }
    }
    cout<<ans.size()<<endl;
    for(int i = 0;i<ans.size();i++) cout<<ans[i]<<endl;
}