#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define INT(...)                                                                                                                                               \
    int __VA_ARGS__;                                                                                                                                           \
    IN(__VA_ARGS__)
#define LL(...)                                                                                                                                                \
    ll __VA_ARGS__;                                                                                                                                            \
    IN(__VA_ARGS__)
#define STR(...)                                                                                                                                               \
    string __VA_ARGS__;                                                                                                                                        \
    IN(__VA_ARGS__)
#define CHR(...)                                                                                                                                               \
    char __VA_ARGS__;                                                                                                                                          \
    IN(__VA_ARGS__)
#define DBL(...)                                                                                                                                               \
    double __VA_ARGS__;                                                                                                                                        \
    IN(__VA_ARGS__)
#define ll long long
#define cout std::cout
#define yes cout<<"Yes"<<"\n"
#define no cout<<"No"<<"\n"
#define rep(i,a,b) for(int i=a;i<b;i++)
#define rrep(i,a,b) for(int i=a;i>=b;i--)
#define fore(i,a) for(auto &i:a)
#define all(x) (x).begin(),(x).end()
#define allr(x) (x).rbegin(),(x).rend()
#define SUM(v) accumulate(all(v), 0LL)
#define MIN(v) *min_element(all(v))
#define MAX(v) *max_element(all(v))
#define lb(c, x) distance((c).begin(), lower_bound(all(c), (x)))
#define ub(c, x) distance((c).begin(), upper_bound(all(c), (x)))
#define pii pair<int, int>
#define pll pair<long long,long long>
#define pb push_back
#define eb emplace_back
#define ff first
#define ss second
#define vi vector<int>
#define vll vector<long long>
#define vc vector<char>
#define vvi vector<vector<int>> 
#define vec(type, name, ...) vector<type> name(__VA_ARGS__)
#define VEC(type, name, size)                                                                                                                                  \
    vector<type> name(size);                                                                                                                                   \
    IN(name)
int scan() { return getchar(); }
void scan(int &a) { cin >> a; }
void scan(long long &a) { cin >> a; }
void scan(char &a) { cin >> a; }
void scan(double &a) { cin >> a; }
void scan(string &a) { cin >> a; }
template <class T, class S> void scan(pair<T, S> &p) { scan(p.first), scan(p.second); }
template <class T> void scan(vector<T> &);
template <class T> void scan(vector<T> &a) {
    for(auto &i : a) scan(i);
}
template <class T> void scan(T &a) { cin >> a; }
void IN() {}
template <class Head, class... Tail> void IN(Head &head, Tail &...tail) {
    scan(head);
    IN(tail...);
}
template <class T> void print(const T &a) { cout << a; }
void OUT() { cout << endl; }
template <class Head, class... Tail> void OUT(const Head &head, const Tail &...tail) {
    print(head);
    if(sizeof...(tail)) cout << ' ';
    OUT(tail...);
}
#define vv(type, name, h, ...) vector<vector<type>> name(h, vector<type>(__VA_ARGS__))
#define VV(type, name, h, w)                                                                                                                                   \
    vector<vector<type>> name(h, vector<type>(w));                                                                                                             \
    IN(name)
#define vvv(type, name, h, w, ...) vector<vector<vector<type>>> name(h, vector<vector<type>>(w, vector<type>(__VA_ARGS__)))
#define vvvv(type, name, a, b, c, ...)                                                                                                                         \
    vector<vector<vector<vector<type>>>> name(a, vector<vector<vector<type>>>(b, vector<vector<type>>(c, vector<type>(__VA_ARGS__))))
template<typename T> using min_priority_queue = priority_queue<T, vector<T>, greater<T>>;
template <class T> pair<T, T> operator-(const pair<T, T> &x, const pair<T, T> &y) { return pair<T, T>(x.ff - y.ff, x.ss - y.ss); }
template <class T> pair<T, T> operator+(const pair<T, T> &x, const pair<T, T> &y) { return pair<T, T>(x.ff + y.ff, x.ss + y.ss); }
template <class T> pair<T, T> operator&(const pair<T, T> &l, const pair<T, T> &r) { return pair<T, T>(max(l.ff, r.ff), min(l.ss, r.ss)); }
template <class T> vector<T> &operator--(vector<T> &v) {
    fore(e, v) e--;
    return v;
}
template <class T> vector<T> operator--(vector<T> &v, int) {
    auto res = v;
    fore(e, v) e--;
    return res;
}
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
#define UNIQUE(x) sort(all(x)), x.erase(unique(all(x)), x.end())
//座標圧縮
template <typename T> void zip(vector<T> &x) {
    vector<T> y = x;
    UNIQUE(y);
    for(int i = 0; i < x.size(); ++i) { x[i] = lb(y, x[i]); }
}
template <class T> T ceil(T x, T y) {
    assert(y >= 1);
    return (x > 0 ? (x + y - 1) / y : x / y);
}
template <class T> T floor(T x, T y) {
    assert(y >= 1);
    return (x > 0 ? x / y : (x + y - 1) / y);
}
long long POW(long long x, int n) {
    long long res = 1LL;
    for(; n; n >>= 1, x *= x)
        if(n & 1) res *= x;
    return res;
}
//0^n=0
long long modpow(long long a, long long n, long long mod) {
    a%=mod;
    assert(a!=0||n!=0);
    if(a==0)return 0;
    long long res = 1;
    while (n > 0) {
        if (n & 1) res = res * a % mod;
        a = a * a % mod;
        n >>= 1;
    }
    return res;
}
//return 0<=a&&a<h&&0<=b&&b<w;
inline bool ingrid(int a,int b,int h,int w){return 0<=a&&a<h&&0<=b&&b<w;}
//return return 0<=a&&a<n;
inline bool inl(int a,int n){return 0<=a&&a<n;}
// bit 演算系
ll pow2(int i) { return 1LL << i; }
int topbit(signed t) { return t == 0 ? -1 : 31 - __builtin_clz(t); }
int topbit(ll t) { return t == 0 ? -1 : 63 - __builtin_clzll(t); }
int lowbit(signed a) { return a == 0 ? 32 : __builtin_ctz(a); }
int lowbit(ll a) { return a == 0 ? 64 : __builtin_ctzll(a); }
// int allbit(int n) { return (1 << n) - 1; }
ll allbit(ll n) { return (1LL << n) - 1; }
int popcount(signed t) { return __builtin_popcount(t); }
int popcount(ll t) { return __builtin_popcountll(t); }
bool ispow2(int i) { return i && (i & -i) == i; }
int in() {
    int x;
    cin >> x;
    return x;
}
ll lin() {
    unsigned long long x;
    cin >> x;
    return x;
}
long long sqrtll(long long x) {
    assert(x >= 0);
    long long rev = sqrt(x);
    while(rev * rev > x) --rev;
    while((rev+1) * (rev+1)<=x) ++rev;
    return rev;
}
int logN(long long n){
    int ret=1;
    while((1LL<<ret)<n)ret++;
    return ret;
}
const double PI=3.1415926535897932384626433832795028841971;
const ll MOD = 998244353;
const int INFI = numeric_limits<int>::max() / 2; const long long INFL = numeric_limits<long long>::max() / 2;
#define inf INFINITY

template<class T>
void debug(vector<T> a){
    rep(i,0,(int)a.size()){
        cout<<a[i]<<' ';
    }
    cout<<endl;
    return;
}

bool palindrome(const string& s){
    return equal(all(s),s.rbegin());
}

template <std::uint_fast64_t Modulus> class modint {
    using u64 = std::uint_fast64_t;
public:
    u64 a;
    constexpr modint(const u64 x = 0) noexcept : a(x % Modulus) {}
    constexpr u64 &val() noexcept { return a; }
    constexpr const u64 &val() const noexcept { return a; }
    constexpr modint operator+(const modint rhs) const noexcept {
        return modint(*this) += rhs;
    }
    constexpr modint operator-(const modint rhs) const noexcept {
        return modint(*this) -= rhs;
    }
    constexpr modint operator*(const modint rhs) const noexcept {
        return modint(*this) *= rhs;
    }
    constexpr modint operator/(const modint rhs) const noexcept {
        return modint(*this) /= rhs;
    }
    constexpr modint &operator+=(const modint rhs) noexcept {
        a += rhs.a;
        if (a >= Modulus) {
            a -= Modulus;
        }
        return *this;
    }
    constexpr modint &operator-=(const modint rhs) noexcept {
        if (a < rhs.a) {
            a += Modulus;
        }
        a -= rhs.a;
        return *this;
    }
    constexpr modint &operator*=(const modint rhs) noexcept {
        a = a * rhs.a % Modulus;
        return *this;
    }
    constexpr modint &operator/=(modint rhs) noexcept {
        u64 exp = Modulus - 2;
        while (exp) {
        if (exp % 2) {
          *this *= rhs;
        }
        rhs *= rhs;
        exp /= 2;
        }
        return *this;
    }
    friend bool operator==(const modint& a,const modint& b) { return a.val()==b.val(); }
    friend bool operator!=(const modint& a,const modint& b) { return a.val()!=b.val(); }
};
using mint9=modint<998244353>;
using mint1=modint<1000000007>;
constexpr pii dx4[4] = {pii{-1, 0}, pii{0, 1}, pii{1, 0}, pii{0, -1}};
constexpr pii dx8[8] = {{1, 0}, {1, 1}, {0, 1}, {-1, 1}, {-1, 0}, {-1, -1}, {0, -1}, {1, -1}};
constexpr pii dx[8] = { {0,1},{1,0}};


#define el "\n"
#define endl "\n"
#define fastio std::cin.sync_with_stdio(false);std::cin.tie(nullptr),cout<<fixed<<setprecision(16);

template<class Abel> struct WeightedUnionFind {
	vector<int> par;
	vector<int> rank;
	vector<Abel> diff_weight;

	WeightedUnionFind(int n = 1, Abel SUM_UNITY = 0) {
		init(n, SUM_UNITY);
	}

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

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

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

	bool issame(int x, int y) {
		return root(x) == root(y);
	}

	bool merge(int x, int y, Abel w) {
		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;
	}

	Abel diff(int x, int y) {
		return weight(y) - weight(x);
	}
};

int main(){
    fastio
    INT(n,m);
    WeightedUnionFind<ll> uf(n);
    struct edge{
        int to,idx;
    };
    vector<vector<edge>> g(n);
    rep(i,0,m){
        INT(u,v);LL(w);
        u--;v--;
        if(uf.issame(u,v)){
            ll d=uf.diff(u,v);
            if(d!=w){
                //爽快な経路
                vi ans;
                [&,dfs{[&,seen{vi(n)}](auto&& self,int pos,int pre=-1)mutable->bool {
                    seen[pos]=1;
                    fore(j,g[pos]){
                        if(j.to==u){
                            ans.pb(j.idx+1);
                            return true;
                        }
                        else if(seen[j.to])continue;
                        else{
                            if(self(self,j.to,pos)){
                                ans.pb(j.idx+1);
                            }
                        }
                    }
                    return false;
                }}]()mutable{
                    dfs(dfs,v);
                }();
                reverse(all(ans));
                ans.pb(i+1);
                //ans=v--->u->v
                if(w<d)reverse(all(ans));
                OUT(ans.size());
                debug(ans);
                return 0;
            }else{
                g[u].pb({v,i});
                g[v].pb({u,i});
            }
        }else{
            uf.merge(u,v,w);
            g[u].pb({v,i});
            g[v].pb({u,i});
        }
    }
    OUT(-1);
	return 0;
}
/*
直進大好きbot
*/