#include <bits/stdc++.h>
using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    long long N,M; cin >> N >> M;
    vector<vector<tuple<long long,long long,long long>>> Graph(N);
    for(long long i=0; i<M; i++){
        long long u,v; cin >> u >> v;
        u--; v--;
        long long w; cin >> w;
        Graph.at(u).push_back({v,i,-w});
        Graph.at(v).push_back({u,i,w});
    }

    vector<bool> already(N);
    vector<long long> dist(N,1e18);
    priority_queue<pair<long long,long long>,vector<pair<long long,long long>>,greater<>> Q;
    dist.at(0) = 0; Q.push({0,0});
    
    long long start = -1;
    while(Q.size()){
        auto [nowd,pos] = Q.top(); Q.pop();
        if(nowd != dist.at(pos)) continue;
        if(already.at(pos)){start = pos; break;}
        already.at(pos) = true;
        
        for(auto [to,epos,w] : Graph.at(pos)){
            if(dist.at(to) > dist.at(pos)+w){
                dist.at(to) = dist.at(pos)+w;
                Q.push({dist.at(to),to});
            }
        }
    }
    if(start == -1){cout << "-1\n"; return 0;}

    dist.assign(N,1e18); already.assign(N,false);
    dist.at(start) = 0;
    while(Q.size()) Q.pop();
    Q.push({0,start});
    vector<pair<long long,long long>> back(N);
    long long start2 = -1;
    vector<long long> route;
    vector<long long> first(N);
    while(Q.size()){
        auto [nowd,pos] = Q.top(); Q.pop();
        if(dist.at(pos) != nowd) continue;
        already.at(pos) = true;
        for(auto [to,epos,w] : Graph.at(pos)){
            if(dist.at(to) > nowd+w){
                if(to == start && nowd+w < 0){
                    route.push_back({epos});
                    start2 = pos; break;
                }
                else if(dist.at(to) > nowd+w && already.at(to) == false){
                    dist.at(to) = nowd+w;
                    Q.push({dist.at(to),to});
                    back.at(to) = {pos,epos};
                }
            }
        }
        if(route.size()) break;
    }
    assert(route.size());
    while(start2 != start){
        route.push_back(back.at(start2).second);
        start2 = back.at(start2).first;
    }

    reverse(route.begin(),route.end());

    cout << route.size() << endl;
    cout << start+1 << endl;
    for(long long i=0; i<route.size(); i++){
        if(i) cout << " ";
        cout << route.at(i)+1;
    }
    cout << endl;
}