#include <bits/stdc++.h>
#define rep(i, n) for(long long i = 0; i < n; i++)
#define ALL(v) (v).begin(), (v).end()
using namespace std;

using lint = long long;

template <class T = long long>
struct WeightedUnionFind {
    private:
    int n;
    vector<int> par, par2, dep;
    vector<T> diff_weight;
    
    public:
    WeightedUnionFind() {}
    WeightedUnionFind(int n_) : n(n_), par(n, -1), par2(n, -1), dep(n, 0), diff_weight(n, T(0)) {}
    
    int leader(int x) {
        assert(0 <= x && x < n);
        if (par[x] < 0) {
            return x;
        } else {
            int r = leader(par[x]);
            diff_weight[x] += diff_weight[par[x]];
            return par[x] = r;
        }
    }
    
    T weight(int x) {
        assert(0 <= x && x < n);
        leader(x);
        return diff_weight[x];
    }
    
    T diff(int x, int y) {
        assert(0 <= x && x < n);
        assert(0 <= y && y < n);
        return weight(y) - weight(x);
    }
    
    int merge(int a, int b, T w) {
        assert(0 <= a && a < n);
        assert(0 <= b && b < n);
        w += weight(a);
        w -= weight(b);
        int x = leader(a);
        int y = leader(b);
        if (x == y) {
            return x;
        }
        if (-par[x] < -par[y]) {
            swap(x, y);
            w *= T(-1);
        }
        par[x] += par[y];
        par[y] = x;
        diff_weight[y] = w;
        par2[b] = a;
        dep[b] = dep[a] + 1;
        return x;
    }
    
    bool same(int x, int y) {
        assert(0 <= x && x < n);
        assert(0 <= y && y < n);
        return leader(x) == leader(y);
    }
    
    int size(int x) {
        assert(0 <= x && x < n);
        return -par[leader(x)];
    }
    
    vector<int> route(int a, int b) {
        assert(0 <= a && a < n);
        assert(0 <= b && b < n);
        int x = (dep[a] < dep[b] ? a : b);
        int y = (dep[a] > dep[b] ? a : b);
        vector<int> res;
        int cur = y;
        while (cur != x) {
            res.emplace_back(cur);
            cur = par2[cur];
        }
        res.emplace_back(x);
        if (res[0] != a) {
            reverse(res.begin(), res.end());
        }
        return res;
    }
    
    vector<vector<int>> groups() {
        vector<vector<int>> member(n);
        for (int i = 0; i < n; i++) {
            member[leader(i)].emplace_back(i);
        }
        vector<vector<int>> res;
        for (int i = 0; i < n; i++) {
            if (member[i].size() > 0) {
                res.emplace_back(member[i]);
            }
        }
        return res;
    }
};

int main() {
    int n, m;
    cin >> n >> m;
    WeightedUnionFind uf(n);
    map<pair<int, int>, int> es;
    rep(i, m) {
        int u, v;
        lint w;
        cin >> u >> v >> w;
        u--;
        v--;
        if (!uf.same(u, v)) {
            uf.merge(v, u, w);
        } else if (uf.diff(v, u) != w) {
            auto r = (uf.diff(v, u) > w ? uf.route(u, v) : uf.route(v, u));
            int sz = r.size();
            cout << sz << endl;
            cout << (uf.diff(v, u) > w ? u + 1 : v + 1) << endl;
            rep(j, sz - 1) {
                cout << es[{r[j], r[j + 1]}] + 1 << " ";
            }
            cout << i + 1 << endl;
            return 0;
        }
        es[{u, v}] = es[{v, u}] = i;
    }
    cout << -1 << endl;
}