#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = 1e9 + 10;
const ll INFL = 4e18;

template <typename Group, auto op, auto e, auto inv>
struct DsuPotentialized {
    DsuPotentialized() = default;
    DsuPotentialized(int n) {
        par = vector<int>(n);
        sz = vector<int>(n);
        diff_weight = vector<Group>(n);
        for (int i = 0; i < n; i++) {
            par[i] = i;
            sz[i] = 1;
            diff_weight[i] = e();
        }
    }
    int find(int x) {
        if (par[x] == x) return x;
        int root = find(par[x]);
        diff_weight[x] = op(diff_weight[x], diff_weight[par[x]]);
        return par[x] = root;
    }
    bool unite(int x, int y, Group w) {
        w = op(w, diff_weight[x]);
        w = op(inv(diff_weight[y]), w);
        x = find(x);
        y = find(y);
        if (x == y) return false;
        if (sz[x] < sz[y]) {
            swap(x, y);
            w = inv(w);
        }
        par[y] = x;
        sz[x] += sz[y];
        diff_weight[y] = w;
        return true;
    }
    bool same(int x, int y) { return find(x) == find(y); }
    Group diff(int x, int y) { return op(diff_weight[y], inv(diff_weight[x])); }
    int size(int x) { return sz[find(x)]; }

private:
    vector<int> par, sz;
    vector<Group> diff_weight;
};

ll op(ll a, ll b) { return a + b; }
ll e() { return 0; }
ll inv(ll a) { return -a; }

int main() {
    int N, M;
    cin >> N >> M;
    DsuPotentialized<ll, op, e, inv> dsu(N);
    vector<vector<pair<int, int>>> G(N);
    for (int i = 0; i < M; i++) {
        int u, v, w;
        cin >> u >> v >> w;
        u--;
        v--;
        if (dsu.same(u, v)) {
            if (dsu.diff(u, v) != w) {
                vector<int> path;
                auto dfs = [&](auto&& dfs, int now, int pre) -> bool {
                    if (now == v) return true;
                    for (auto [nxt, id] : G[now]) {
                        if (nxt == pre) continue;
                        if (dfs(dfs, nxt, now)) {
                            path.push_back(id);
                            return true;
                        }
                    }
                    return false;
                };
                dfs(dfs, u, -1);
                path.push_back(i);
                if (dsu.diff(u, v) < w) ranges::reverse(path);
                cout << ssize(path) << endl;
                cout << u + 1 << endl;
                for (int x : path) cout << x + 1 << ' ';
                cout << endl;
                return 0;
            }
        }
        dsu.unite(u, v, w);
        G[u].push_back({v, i});
        G[v].push_back({u, i});
    }

    cout << -1 << endl;
}