#include <bits/stdc++.h>
using namespace std;
#define int long long
vector<int>g[202000];
vector<pair<int,int>>v[202000];
int r[2020000],a[202000];
void dfs(int u,int f){
	if(a[u])return;
	int x=0;
	for(auto v:g[u]){
		if(v==f)continue;
		dfs(v,u);
		// x+=a[v];
	}
	for(auto it:v[u]){
		x=max(a[it.first]+a[it.second],x);
	}
	a[u]=x;
}
void solve(){
	int n,m,f=1;cin>>n>>m;
	while(m--){
		int x,y,z;cin>>x>>y>>z;
		g[x].push_back(y);
		g[x].push_back(z);
		g[y].push_back(x);
		g[z].push_back(x);
		v[x].push_back({z,y});
		r[x]+=2;
	}	
	queue<int>q;
	vector<int>res;
	for(int i=1;i<=n;i++){
		if(r[i]==0){
			q.push(i);
			a[i]=1;
		}
	}
	while(q.size()){
		int p=q.front();q.pop();
		res.push_back(p);
		for(auto it:g[p]){
			r[it]--;
			if(r[it]==0)
				q.push(it);
		}
	}
	if(res.size()!=n){
		cout<<-1<<'\n';
	}else{
		int ans=0;
		f=res.back();
		for(int i=1;i<=n;i++){
			if(!a[i]){
				dfs(i,-1);
			}
		}
		for(int i=1;i<=n;i++)
			ans+=a[i];
		if(ans>1e9){
			cout<<-1;
		}else
			cout<<ans;
	}
}
signed main(){
	ios_base::sync_with_stdio(0);
	cin.tie(0),cout.tie(0);
	int t=1;
	// cin>>t;
	while(t--){
		solve();
	}
}