#include <atcoder/all>
#include <bits/stdc++.h>
#define rep(i, a, b) for (ll i = (ll)(a); i < (ll)(b); i++)
using namespace atcoder;
using namespace std;

typedef long long ll;

struct UnionFindWeight {
    vector<ll> par;
    vector<ll> rank;
    vector<ll> diff_weight;

    UnionFindWeight(ll n = 1, ll SUM_UNITY = 0) { reset(n, SUM_UNITY); }

    void reset(ll n = 1, ll SUM_UNITY = 0) {
        par.resize(n);
        rank.resize(n);
        diff_weight.resize(n);
        for (ll i = 0; i < n; ++i)
            par[i] = i, rank[i] = 0, diff_weight[i] = SUM_UNITY;
    }

    ll root(ll x) {
        if (par[x] == x) {
            return x;
        } else {
            ll r = root(par[x]);
            diff_weight[x] += diff_weight[par[x]];
            return par[x] = r;
        }
    }

    ll weight(ll x) {
        root(x);
        return diff_weight[x];
    }

    bool same(ll x, ll y) { return root(x) == root(y); }

    bool unite(ll x, ll y, ll w) { // x ----(距離 w)---- y
        w += weight(x);
        w -= weight(y);
        x = root(x);
        y = root(y);
        if (x == y)
            return false;
        if (rank[x] < rank[y])
            swap(x, y), w = -w;
        if (rank[x] == rank[y])
            ++rank[x];
        par[y] = x;
        diff_weight[y] = w;
        return true;
    }

    ll dist(ll x, ll y) { return weight(y) - weight(x); }
};

template <typename T> struct Graph {
    struct edge {
        int to;
        T cost;
    };
    int N;
    vector<vector<edge>> G;
    vector<T> dist;
    vector<int> prever;

    Graph(int n) { init(n); }
    T inf() {
        if (is_same_v<T, int>)
            return 1e9;
        else
            return 1e18;
    }
    T zero() { return T(0); }

    void init(int n) {
        N = n;
        G.resize(N);
        dist.resize(N, inf());
    }
    void add_edge(int s, int t, T cost) {
        edge e;
        e.to = t, e.cost = cost;
        G[s].push_back(e);
    }
    void dijkstra(int s) {
        rep(i, 0, N) dist[i] = inf();
        prever = vector<int>(N, -1);
        dist[s] = zero();
        priority_queue<pair<T, int>, vector<pair<T, int>>,
                       greater<pair<T, int>>>
            q;
        q.push({zero(), s});
        while (!q.empty()) {
            int now;
            T nowdist;
            tie(nowdist, now) = q.top();
            q.pop();
            if (dist[now] < nowdist)
                continue;
            for (auto e : G[now]) {
                T nextdist = nowdist + e.cost; // 次の頂点への距離
                if (dist[e.to] > nextdist) {
                    prever[e.to] = now;
                    dist[e.to] = nextdist;
                    q.push({dist[e.to], e.to});
                }
            }
        }
    }

    vector<int> get_path(int t) { // tへの最短路構築
        if (dist[t] >= inf())
            return {-1};
        vector<int> path;
        for (; t != -1; t = prever[t]) {
            path.push_back(t);
        }
        reverse(path.begin(), path.end());
        return path;
    }
};

int main() {
    int n, m;
    cin >> n >> m;
    UnionFindWeight uf(n);
    Graph<int> gr(n);
    map<pair<int, int>, int> ma;
    rep(i, 0, m) {
        int l, r, d;
        cin >> l >> r >> d;
        l--;
        r--;
        if (uf.same(l, r)) {
            if (uf.dist(l, r) != d) {
                if (uf.dist(l, r) < d) {
                    swap(l, r);
                }
                gr.dijkstra(l);
                auto path = gr.get_path(r);
                vector<int> ans;
                rep(j, 0, path.size() - 1) {
                    ans.push_back(ma[{path[j], path[j + 1]}]);
                }
                ans.push_back(i);
                cout << ans.size() << endl;
                cout << l + 1 << endl;
                rep(j, 0, ans.size()) { cout << ans[j] + 1 << ' '; }
                cout << endl;
                return 0;
            }
        } else {
            uf.unite(l, r, d);
            gr.add_edge(l, r, 1);
            gr.add_edge(r, l, 1);
            ma[{l, r}] = i;
            ma[{r, l}] = i;
        }
    }
    cout << "-1" << endl;
}