#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define ALL(v) v.begin(),v.end()
#define dbg(x) cerr << #x << ": " << (x) << endl;
int n,m;
vector<array<int,4>> e;
struct WUF {
    WUF(int n) {
        par.resize(n);
        iota(par.begin(), par.end(), 0);
		rank.assign(n, 1);
        w.resize(n, 0);
    }
    // 根ノード
    int root(int x) {
        if (par[x] == x) return x;
        int rx = root(par[x]);
        w[x] += w[par[x]];
        return par[x] = rx;
    }

    // weight(y) = weight(x) + dwとなるように結合
    bool unite(int x, int y, ll dw) {
        dw += weight(x); dw -= weight(y);
        x = root(x); y = root(y);
        if (x == y) return false;
        if (rank[x] < rank[y]) swap(x,y), dw = -dw;
        if (rank[x] == rank[y]) ++rank[x];
        par[y] = x;
        w[y] = dw;
        return true;
    }

    // 同じ集合に所属するか
    bool same(int x, int y) {
        return root(x) == root(y);
    }
    // 親ノードを0とするときの重み
    long long weight(int x) {
        root(x);
        return w[x];
    }
    // 頂点xと頂点yの重みの差
    // 制約：xとyが連結
    long long diff(int x, int y) {
        return weight(y) - weight(x);
    }

    vector<vector<int>> groups() {
        vector<vector<int>> gr(par.size());
        for (int v = 0; v < par.size(); ++v) {
            gr[root(v)].push_back(v);
        }
        
        vector<vector<int>> res;
        for (int v = 0; v < (int)par.size(); ++v) {
            if (gr[v].size()) res.push_back(gr[v]);
        }
        return res;
    }
    vector<int> par;
	vector<int> rank;
    vector<ll> w;
};
int main() {
    cin >> n >> m;
    e.resize(m);
    for (int i = 0; i < m; ++i) {
        auto& [u,v,w,id] = e[i];
        cin >> u >> v >> w;
        --u; --v;
        id = i;
    }
    vector<vector<pair<int,int>>> g(n);
    WUF uf(n);
    for (auto&& [u,v,w,i] : e) {
        // check;
        // for (int j = 0; j < n; ++j) {
        //     cerr << uf.weight(j) << " \n"[j==n-1];
        // }
        if (uf.same(u,v)) {
            if (uf.diff(u,v) == w) {
                /// ok
            }
            else {
                // bfs
                queue<int> q;
                vector<pair<int,int>> pre(n, {-1,-1});
                q.push(u);
                pre[u] = {-2, -2};
                while (q.size()) {
                    int pos = q.front(); q.pop();
                    for (auto [to,id] : g[pos]) {
                        if (pre[to].first == -1) {
                            pre[to].first = pos;
                            pre[to].second = id;
                            q.push(to);
                        }
                    }
                }
                // reconstruct
                vector<int> path;
                int now = v;
                while (pre[now].second != -2) {
                    path.push_back(pre[now].second);
                    now = pre[now].first;
                }
                path.push_back(i);

                // plus, minus
                now = v;
                ll sum = 0;
                for (int ei : path) {
                    auto&& [a,b,w,id] = e[ei];
                    if (now == a) {
                        sum += w;
                        now = b;
                    }
                    else {
                        sum -= w;
                        now = a;
                    }
                }
                int start = v;
                if (sum < 0) {
                    reverse(ALL(path));
                }

                // out
                cout << path.size() << '\n';
                cout << start+1 << '\n';
                for (int j = 0; j < path.size(); ++j) {
                    cout << path[j]+1 << " \n"[j==path.size()-1];
                }
                return 0;
            }
        }
        else {
            uf.unite(u, v, w);
            g[u].emplace_back(v, i);
            g[v].emplace_back(u, i);
        }
    }
    cout << "-1\n";
}