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

void fast_io() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
}

int main() {
    fast_io();
    int n, m;
    cin >> n >> m;
    vector<vector<tuple<int, long long, int>>> g(n);
    for (int i = 1; i <= m; i++) {
        int u, v, w;
        cin >> u >> v >> w;
        u--, v--;
        g[u].push_back({v, w, i});
        g[v].push_back({u, -w, i});
    }
    vector<bool> vis(n);
    vector<long long> potential(n);
    vector<pair<int, int>> par(n);
    for (int i = 0; i < n; i++) {
        if (vis[i]) {
            continue;
        }
        deque<int> dq;
        dq.push_back(i);
        vis[i] = true;
        par[i] = {-1, -1};
        while (!dq.empty()) {
            int u = dq.front();
            dq.pop_front();
            for (auto [v, w, i] : g[u]) {
                if (!vis[v]) {
                    vis[v] = true;
                    par[v] = {u, i};
                    potential[v] = potential[u] + w;
                    dq.push_back(v);
                    continue;
                }
                if (potential[v] == potential[u] + w) {
                    continue;
                }
                if (potential[v] < potential[u] + w) {
                    swap(u, v);
                }
                vector<int> path_u, path_v;
                int x = u, y = v;
                while (x != -1) {
                    path_u.push_back(par[x].second);
                    x = par[x].first;
                }
                while (y != -1) {
                    path_v.push_back(par[y].second);
                    y = par[y].first;
                }
                while (!path_u.empty() && !path_v.empty() &&
                       path_u.back() == path_v.back()) {
                    path_u.pop_back();
                    path_v.pop_back();
                }
                vector<int> ans = path_u;
                reverse(path_v.begin(), path_v.end());
                ans.insert(ans.end(), path_v.begin(), path_v.end());
                ans.push_back(i);
                int M = ans.size();
                cout << M << endl;
                cout << u + 1 << endl;
                for (int i = 0; i < M; i++) {
                    cout << ans[i] << (i + 1 == M ? "\n" : " ");
                }
                return 0;
            }
        }
    }
    cout << -1 << endl;
}