#include <bits/stdc++.h>
using namespace std;

#define fileio() freopen("input.txt","r",stdin); freopen("output.txt","w",stdout)
#define fio() ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define all(x) (x).begin(), (x).end()
#define allr(x) x.rbegin(), x.rend()
#define cmprs(x) sort(all(x)),x.erase(unique(all(x)),x.end())
#define endl "\n"
#define sp " "
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define F first
#define S second
#define rz resize
#define sz(a) (int)(a.size())
#define clr(a) a.clear()

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, ll> pil;
typedef tuple<int, int, int> tpi;
typedef tuple<ll, ll, ll> tpl;
typedef pair<double, ll> pdl;
typedef pair<double, int> pdi;

const int dx[] = {1,-1,0,0,1,1,-1,-1};
const int dy[] = {0,0,1,-1,1,-1,1,-1};
const ll MOD = 1e9+7;
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3f;
const int MAX = 202020; // PLZ CHK!

typedef array<ll,4> arr;

struct dsu {
    vector<int> p;
    int n;
    void init(int _n) {
        n=_n+10;
        p.resize(n);
        iota(all(p),0);
    }

    int fd(int a) {
        if (a==p[a]) return a;
        return p[a]=fd(p[a]);
    }

    int mg(int a, int b) {
        a=fd(a), b=fd(b);
        if (a==b) return 0;
        p[b]=a; return 1;
    }
} dsu1, dsu2;

int N,M;
arr E[MAX],E2[MAX];
int usd[MAX],par[MAX][20],cst[MAX][20],dep[MAX];
vector<pii> G[MAX];

void dfs(int cur, int prv) {
    for (auto [nxt,val]:G[cur]) {
        if (nxt==prv) continue;
        par[nxt][0]=cur, cst[nxt][0]=val;
        dep[nxt]=dep[cur]+1;
        dfs(nxt,cur);
    }
}

void init() {
    for (int j=1; j<20; j++) {
        for (int i=1; i<=N; i++) {
            par[i][j]=par[par[i][j-1]][j-1];
            cst[i][j]=max(cst[i][j-1],cst[par[i][j-1]][j-1]);
        }
    }
}

int lca(int u, int v) {
    int t1=u,t2=v;
    int res=0;
    if (dep[u]>dep[v]) swap(u,v);
    for (int i=19; i>=0; i--) {
        if (dep[par[v][i]]>=dep[u]) {
            res=max(res, cst[v][i]);
            v=par[v][i];
        }
    }
    
    if (u==v) {
        return res;
    }

    for (int i=19; i>=0; i--) {
        if (par[v][i]!=par[u][i]) {
            res=max(res, cst[v][i]);
            res=max(res, cst[u][i]);

            v=par[v][i];
            u=par[u][i];
        }
    }
    return max({res, cst[u][0], cst[v][0]});
}

int main() {
    fio();
    cin>>N>>M;
    for (int i=0; i<M; i++) {
        int u,v,w; cin>>u>>v>>w;
        E[i]={u,v,w,i};
        E2[i]=E[i];
    }

    dsu1.init(N+1),dsu2.init(N+1);
    sort(E,E+M,[](auto a, auto b){ return a[2]<b[2]; });

    for (int i=0,c=0; i<M && c<N-1; i++) {
        auto [u,v,w,idx]=E[i];
        if (dsu1.mg(u,v)) {
            usd[idx]=1;
            c++;
        }
    }

    for (int i=0,c=0; i<M && c<N-1; i++) {
        auto [u,v,w,idx]=E[i];
        if (usd[idx]) continue;
        if (dsu2.mg(u,v)) {
            G[u].pb({v,w}), G[v].pb({u,w});
            c++;
        }
        if (i==M-1 && c<N-1) {
            cout<<-1;
            return 0;
        }
    }

    dfs(1,0);
    init();

    ll ans=0;
    for (int i=0; i<M; i++) {
        auto [u,v,w,idx]=E2[i];
        if (usd[i]) {
            ll t=lca(u,v)+1;
            ans+=max(0ll,t-w);
        }
    }

    cout<<ans;
    
    return 0;
}