#include<bits/stdc++.h>
using namespace std;
using ll=long long;
using ldb=long double;
using ull=unsigned long long;
const long long inf=0x3f3f3f3f3f3f3f3f;
using i128=__int128;
const int mod=1000000007;
const long double eps=0.00000000001;

struct DSU
{
    vector<ll>f,siz;
    DSU() {}
    DSU(ll n)
    {
        init(n);
    }

    void init(ll n)
    {
        f.resize(n);
        std::iota(f.begin(), f.end(), 0);
        siz.assign(n, 1);
    }

    ll find(ll x)
    {
        while(x!=f[x])
        {
            x=f[x]=f[f[x]];
        }
        return x;
    }

    bool same(ll x, ll y)
    {
        return find(x)==find(y);
    }

    bool merge(ll x,ll y)
    {
        x=find(x);
        y=find(y);
        if(x==y)
        {
            return false;
        }
        siz[x]+=siz[y];
        f[y]=x;
        return true;
    }

    ll size(ll x)
    {
        return siz[find(x)];
    }
};

vector<pair<ll,ll>>a[200010];
ll ans[200010];
DSU c;

void dfs(ll p)
{
    if(a[p].empty())
    {
        ans[p]=1;
        return;
    }
    ll la=(ll)a[p].size();
    ll mx=-inf;
    for(ll i=0;i<=la-1;i++)
    {
        ll x=a[p][i].first;
        ll y=a[p][i].second;
        if(ans[x]==-1)dfs(x);
        if(ans[y]==-1)dfs(y);
        mx=max(mx,ans[x]+ans[y]);
    }
    ans[p]=mx;
}


void solve()
{
    ll n,m;
    cin>>n>>m;
    c.init(n+10);
    ll f=0;
    for(ll i=0;i<=n;i++)ans[i]=-1;
    for(ll i=1;i<=m;i++)
    {
        ll x,y,z;
        cin>>x>>y>>z;
        ll fax=c.find(x);
        if(fax==y)f=-1;
        if(fax==z)f=-1;
        c.merge(x,y);
        c.merge(x,z);
        a[x].push_back({y,z});
    }
    if(f==-1)
    {
        printf("-1\n");
        return;
    }
    for(ll i=1;i<=n;i++)dfs(i);
    ll sum=0;
    for(ll i=1;i<=n;i++)
    {
        sum+=ans[i];
    }
    printf("%lld\n",sum);


}

int main()
{
    ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
    ll _=1;
//    cin>>_;
    while(_--)
    {
        solve();
    }
    return 0;
}