#include <bits/stdc++.h>

using namespace std;
#define int long long
const int p=998244353;
int po(int a,int b) {if(b==0) return 1; if(b==1) return a; if(b%2==0) {int u=po(a,b/2);return (u*1LL*u)%p;} else {int u=po(a,b-1);return (a*1LL*u)%p;}}
int inv(int x) {return po(x,p-2);}
mt19937 rnd;
#define app push_back
#define all(x) (x).begin(),(x).end()
#ifdef LOCAL
#define debug(...) [](auto...a){ ((cout << a << ' '), ...) << endl;}(#__VA_ARGS__, ":", __VA_ARGS__)
#define debugv(v) do {cout<< #v <<" : {"; for(int izxc=0;izxc<v.size();++izxc) {cout << v[izxc];if(izxc+1!=v.size()) cout << ","; }cout <<"}"<< endl;} while(0)
#else
#define debug(...)
#define debugv(v)
#endif
#define lob(a,x) lower_bound(all(a),x)
#define upb(a,x) upper_bound(all(a),x)
const int maxn=1e5+5;
map<pair<int,int>,int> ed;map<pair<int,int>,int> id;
vector<pair<int,int> > g[maxn];
bool used[maxn];
int pr[maxn];int pot[maxn];
void solve2(vector<int> v)
{
    int sum=0;
    for(int i=0;i<v.size();++i)
    {
        sum+=ed[{v[i],v[(i+1)%v.size()]}];
    }
    if(sum<0) {sum*=(-1);reverse(all(v));}
    assert(sum);
    cout<<v.size()<<'\n';
    cout<<v[0]+1<<'\n';
    for(int i=0;i<v.size();++i)
    {
        cout<<id[{v[i],v[(i+1)%v.size()]}]+1<<' ';
    }
    exit(0);
}
void solve(int x,int y)
{
    debug(x,y);
    vector<int> vx,vy;
    vx.app(x);vy.app(y);
    while(pr[vx.back()]!=(-1)) {vx.app(pr[vx.back()]);}
    while(pr[vy.back()]!=(-1)) {vy.app(pr[vy.back()]);}
    debugv(vx);debugv(vy);
    map<int,int> posx;for(int i=0;i<vx.size();++i) {posx[vx[i]]=i;}
    vector<int> h;
    for(int i=0;i<vy.size();++i)
    {
        if(posx.count(vy[i]))
        {
            int j=posx[vy[i]];
            for(int s=j;s>=0;--s)
            {
                h.app(vx[s]);
            }
            solve2(h);
        }
        else
        {
            h.app(vy[i]);
        }
    }
    assert(false);
}
void dfs(int x)
{
    used[x]=true;
    for(auto [v,w]:g[x])
    {
        if(!used[v])
        {
            pr[v]=x;
            pot[v]=pot[x]+w;
            dfs(v);
        }
        else
        {
            if(pot[v]!=pot[x]+w)
            {
                solve(x,v);
            }
        }
    }
}
int32_t main()
{
    ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    fill(pr,pr+maxn,-1);
    int n,m;cin>>n>>m;
    for(int i=0;i<m;++i)
    {
        int x,y,w;cin>>x>>y>>w;--x;--y;
        if(ed.count({x,y}) && ed[{x,y}]==w)
        {
            continue;
        }
        else if(ed.count({x,y}))
        {
            if(ed[{x,y}]-w>0)
                {
                    cout<<2<<'\n'<<x+1<<'\n'<<id[{x,y}]+1<<' '<<i+1<<endl;
                    return 0;
                }
                else {
                    cout<<2<<'\n'<<x+1<<'\n'<<i+1<<' '<<id[{x,y}]+1<<endl;
                    return 0;
                }
        }
        ed[{x,y}]=w;ed[{y,x}]=(-w);
        g[x].app({y,w});g[y].app({x,-w});id[{x,y}]=i;id[{y,x}]=i;
    }
    for(int i=0;i<n;++i)
    {
        if(!used[i]) {dfs(i);}
    }
    cout<<(-1);
    return 0;
}