#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
// using namespace __gnu_pbds;
// #define ordered_set tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update>
// #define ordered_multiset tree<int, null_type, less_equal<int>, rb_tree_tag,tree_order_statistics_node_update>
using namespace std;
void _main();
int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	_main();
	return 0;
}
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using vi = std::vector<int>;
using vvi = std::vector<vi>;
using vl = std::vector<ll>;
using vii = std::vector<pair<int, int> >;
using vvl = std::vector<vl>;
using vll = std::vector<pair<ll , ll> >;
using vd = std::vector<double>;
using vvd = std::vector<vd>;
using vs = std::vector<std::string>;
using vvs = std::vector<vs>;
using vb = std::vector<bool>;
using vvb = std::vector<vb>;
using vc = std::vector<char>;
using vvc = std::vector<vc>;
using pii = std::pair<int, int>;
using pll = std::pair<ll, ll>;
using piil = std::pair<pair<int, int>, ll>;
using mii = std::map<int, int>;
using mll = std::map<ll, ll>;
using pql = std::priority_queue<ll>;
using pqi = std::priority_queue<int>;
using pqiil = std::priority_queue<pair<pair<int, int>, ll> >;
using pqii = std::priority_queue<pair<int, int> >;

#define pb push_back
#define ps push
#define eb emplace_back
#define is insert
#define er erase
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define sf(i) sizeof(i)
#define endl "\n"
#define sz(v) ((int)(v).size())
#define all(v) (v).begin(), (v).end()
#define rep(i, L, R) for(ll i = L;i<=R;i++)
#define pcis precision

template<typename T>
struct infinity {
	static constexpr T max=std::numeric_limits<T>::max();
	static constexpr T min=std::numeric_limits<T>::min();
	static constexpr T value=std::numeric_limits<T>::max()/2;
	static constexpr T mvalue=std::numeric_limits<T>::min()/2;
};
template<typename T>constexpr T INF=infinity<T>::value;
constexpr ll lINF=INF<ll>;
constexpr int iINF = INF<int>;
constexpr ld PI = 3.1415926535897932384626;

bool vst[100001];
vector<pair<ll, pll>> adj[100001];
ll A[100001];
ll at = -1;
ll at2 = -1;
ll at3 = 0;
vll adj2[100001];
void DFS(ll node, ll atai) {
	vst[node] = true;
	A[node] = atai;
	if (at != -1)return;
	for (auto ss : adj[node]) {
		ll i = ss.f;
		auto[ cst, num] = ss.s;
		if (vst[i]) {
			if (A[i] != atai+cst) {
				if (at == -1) {
					if (atai+cst > A[i]) {
						at = node;
						at2 = i;// at -> at2임
						at3 = num;
						return;
					} else {
						// 반대로 돌아야함
						at = i;
						at2 = node;// at2 -> at임
						at3 = num;
						return;
					}
				}
			}
		} else {
			adj2[node].pb({i, num});
			adj2[i].pb({node, num});
			DFS(i, cst+atai);
		}
	}
	return;
}

// at2에서 시작하면 됨

vl lst;
bool DFS2(ll node, ll par) {
	if (node == at) {
		return true;
	}
	for (auto [i, num] : adj2[node]) {
		if (i==par)continue;
		if (DFS2(i, node)) {
			lst.pb(num);
			return true;
		}
	}
}

void _main() {

	ll N, M;
	cin >> N >> M;

	for (ll i = 1; i<=M; i++) {
		ll a, b, c;
		cin >>a >> b >> c;
		adj[a].pb({b,{c,i}});
		adj[b].pb({a,{-c,i}});
	}


	DFS(1, 0);

	if (at == -1) {
		cout << -1 << endl;
		return;
	}
	DFS2(at2, -1);
	reverse(all(lst));
	lst.pb(at3);
	cout << lst.size() << endl;
	cout << at2 << endl;

	for (auto i : lst) {
		cout << i << " ";
	}
	cout << endl;










}