#include<bits/stdc++.h>
#include<atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long int ll;
typedef long double ld;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<vvvi> vvvvi;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<vvb> vvvb;
typedef vector<vvvb> vvvvb;
typedef pair<ll,ll> pi;
typedef pair<ll,pi> ppi;
typedef pair<ll,ppi> pppi;
typedef pair<ll,pppi> ppppi;
#define FOR(i,l,r) for(ll i=l;i<r;i++)
#define REP(i,n) FOR(i,0,n)
#define RFOR(i,l,r) for(ll i=r-1;i>=l;i--)
#define RREP(i,n) RFOR(i,0,n)
#define ALL(x) x.begin(),x.end()
#define F first
#define S second
#define BS(A,x) binary_search(ALL(A),x)
#define LB(A,x) (ll)(lower_bound(ALL(A),x)-A.begin())
#define UB(A,x) (ll)(upper_bound(ALL(A),x)-A.begin())
#define COU(A,x) (UB(A,x)-LB(A,x))
#define sz(c) ((ll)(c).size())
/*
#include<boost/multiprecision/cpp_int.hpp>
namespace mp=boost::multiprecision;
using Bint=mp::cpp_int;
*/
template<typename T>using min_priority_queue=priority_queue<T,vector<T>,greater<T>>;
template<typename T1,typename T2>ostream&operator<<(ostream&os,pair<T1,T2>p){os<<p.F<<" "<<p.S;return os;}
template<typename T1,typename T2>istream&operator>>(istream&is,pair<T1,T2>&p){is>>p.F>>p.S;return is;}
template<typename T>ostream&operator<<(ostream&os,vector<T>v){REP(i,sz(v))os<<v[i]<<(i+1!=sz(v)?" ":"");return os;}
template<typename T>istream&operator>>(istream&is,vector<T>&v){for(T&in:v)is>>in;return is;}
template<class T>bool chmax(T&a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T>bool chmin(T&a,T b){if(b<a){a=b;return 1;}return 0;}
ld dist(ld x1,ld y1,ld x2,ld y2){return sqrtl((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));}
vi fast_mod_convolution(vi&a,vi&b,ll mod){
  const ll m1=167772161,m2=469762049,m3=1224736769;
  const ll m1_inv_m2=inv_mod(m1,m2);
  const ll m12_inv_m3=inv_mod(m1*m2,m3);
  const ll m12_mod=m1*m2%mod;
  auto x=convolution<m1>(a,b);
  auto y=convolution<m2>(a,b);
  auto z=convolution<m3>(a,b);
  vector<ll>ret(sz(a)+sz(b)-1);
  REP(i,sz(ret)){
    ll v1=(y[i]-x[i])*m1_inv_m2%m2;if(v1<0)v1+=m2;
    ll v2=(z[i]-(x[i]+m1*v1)%m3)*m12_inv_m3%m3;if(v2<0)v2+=m3;
  	ret[i]=(x[i]+m1*v1+m12_mod*v2)%mod;
  }
  return ret;
}
const ld EPS=1e-8;
//*
using mint=modint998244353;
const ll mod=998244353;
//*/
/*
using mint=modint1000000007;
const ll mod=1000000007;
//*/
//using mint=modint;
//*
typedef vector<mint> vm;
typedef vector<vm> vvm;
typedef vector<vvm> vvvm;
typedef vector<vvvm> vvvvm;
ostream&operator<<(ostream&os,mint a){os<<a.val();return os;}
istream&operator>>(istream&is,mint&a){int x;is>>x;a=mint(x);return is;}
//*/
int main(){
  ll N,M;cin>>N>>M;
  vi U(M),V(M),W(M);
  vector<vector<pi>>E(N);
  REP(i,M){
  	ll u,v,w;cin>>u>>v>>w;u--;v--;
  	E[u].emplace_back(pi(v,i));
  	E[v].emplace_back(pi(u,-i-1));
  	U[i]=u;V[i]=v;W[i]=w;
  }
  vi D(N,1e18),P(N),pre(N),depth(N);
  REP(i,N)if(D[i]>1e17){
  	D[i]=0;P[i]=N;pre[i]=i;
  	queue<ll>Q;
  	Q.emplace(i);
  	while(sz(Q)){
  		ll v=Q.front();Q.pop();
  		for(auto[u,idx]:E[v]){
  			ll c=(idx>=0?W[idx]:-W[-1-idx]);
  			if(D[u]>1e17){
  				depth[u]=depth[v]+1;
  				P[u]=idx;
  				D[u]=D[v]+c;
  				pre[u]=v;
  				Q.emplace(u);
  			}
  			else if(D[u]!=D[v]+c){
  				ll w;
  				{
  					ll _u=u,_v=v;
  					while(_u!=_v){
  						if(depth[_u]>depth[_v])_u=pre[_u];
  						else _v=pre[_v];
  					}
  					w=_u;
  				}
  				vi A,B;
  				for(int i=u;i!=w;i=pre[i])A.emplace_back(max(P[i],-1-P[i])+1);
  				for(int i=v;i!=w;i=pre[i])B.emplace_back(max(P[i],-1-P[i])+1);
  				vi ans;ll s;
  				if(D[u]>D[v]+c){
  					s=v+1;
  					ans=B;
  					reverse(ALL(A));
  					ans.insert(ans.end(),ALL(A));
  					ans.emplace_back(max(idx,-1-idx)+1);
  				}
  				else{
  					s=u+1;
  					ans=A;
  					reverse(ALL(B));
  					ans.insert(ans.end(),ALL(B));
  					ans.emplace_back(max(idx,-1-idx)+1);
  				}
  				cout<<sz(ans)<<endl<<s<<endl<<ans<<endl;
  				return 0;
  			}
  		}
  	}
  }
  cout<<-1<<endl;
  return 0;
}