#include <bits/stdc++.h>
using namespace std;
int main () {
	int N, M;
	cin >> N >> M;
	using ll = long long;
	using T = tuple<int, int, ll>;
	std::vector<T> gr[200020];
	int E[200020];
	for (int i = 1; i <= M; i ++) {
		int u, v;
		ll w;
		cin >> u >> v >> w;
		gr[u].emplace_back(v, i, w);
		gr[v].emplace_back(u, i, -w);
		E[i] = u ^ v;
	}
	ll D[200020];
	int pre [200020];
	fill(D, D + (N + 1), 0);
	fill(pre, pre + (N + 1), 0);
	for (int i = 1; i <= N; i ++) {
		if (pre[i]) continue;
		pre[i] = -1;
		queue<int>que;
		que.push(i);
		int beg = -1;
		int pr2 = -1;
		ll d2 = -1;
		while (!que.empty()) {
			int u = que.front();
			que.pop();
			for (auto& [v, p, d] : gr[u]) {
			    // cout << v << " " << i << " " << d << endl;
				if (!pre[v]) {
					pre[v] = p;
					D[v] = D[u] + d;
					que.push(v);
				} else if (D[v] != D[u] + d) {
					beg = v;
					pr2 = p;
					d2 = D[u] + d;
					break;
				}
			}
			if (beg != -1) break;
		}
		if (0) {
		    for (int j = 1; j <= N; j ++) {
			cout << D[j] << " ";
		    }
		    cout << endl;
		}
		if (beg != -1) {
			ll d1 = D[beg];
			vector<int> a1, a2;
			int fl = beg;
			while (fl != i) {
				a1.push_back(pre[fl]);
				fl = fl ^ E[pre[fl]];
			}
			a2.push_back(pr2);
			fl = beg ^ E[pr2];
			while (fl != i) {
				a2.push_back(pre[fl]);
				fl = fl ^ E[pre[fl]];
			}
			if (d1 > d2) {
				swap(a1, a2);
			}
			reverse(a2.begin(), a2.end());
			for (auto& a : a2) {
				a1.push_back(a);
			}
			bool ex[200020];
			a2.clear();
			for (auto& a : a1) {
			    // cout << a<< " ";
				if (ex[a]) {
					while (ex[a]) {
						ex[a2.back()] = false;
						a2.pop_back();
					}
				} else {
					ex[a] = true;
					a2.push_back(a);
				}
			}
			cout << a2.size() << endl;
			cout << beg << endl;
			for (int i = 0; i < a2.size(); i ++) {
				cout << a2[i] << (i + 1 < a2.size() ? " " : "");
			}
			cout << endl;
			return 0;
		}
	}
	puts("-1");
}