#pragma GCC optimize("Ofast", "unroll-loops", "no-stack-protector")
#include <bits/stdc++.h>
#define pb push_back
#define MP make_pair
#define F first
#define S second
#define mem(x, y) memset((x), (y), sizeof(x))
#define loli ios::sync_with_stdio(0), cin.tie(0);
#define ALL(x) (x).begin(), (x).end()
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
template<typename Ta, typename Tb>istream& operator>>(istream &in, pair<Ta, Tb> &p){ return in >> p.first >> p.second; }
template<typename Ta, typename Tb>ostream& operator<<(ostream &out, pair<Ta, Tb> &p){ return out << "(" << p.first << ", " << p.second << ")"; }
template<typename T>void arr_print(T a, T b){ T i = a; for(cout << *i++; i != b; i++) cout << " " << *i; cout << "\n"; }
ostream& print(){ return cout << "\n"; }
template<typename T>ostream& print(T a){ return cout << a << "\n"; }
template<typename T, typename... Args>ostream& print(T a, Args ...args){ cout << a << " "; return print(args...); }

//--------------------Main Code--------------------

struct edge{
	int u, v, w;
	bool operator<(const edge &a)const{
		return w < a.w;
	}
} a[200000];

vector<edge> edges;

vector<pii> v[100001];

bitset<100001> vis;
bitset<200000> used;

int n, boss[100001], sz[100001], mxson[100001], fa[100001], lt[100001], dep[100001], tr[400000], idx[100001], inc = 1;

int find(int x){
	if(boss[x] == x)
		return x;
	return boss[x] = find(boss[x]);
}

void combine(int a, int b){
	boss[find(a)] = find(b);
}

void modify(int rt, int lb, int rb, int x, int k){
	int m = lb + rb >> 1;
	if(lb == x && rb == x)
		return tr[rt] = k, void();
	if(x <= m)
		modify(rt << 1, lb, m, x, k);
	else
		modify(rt << 1 | 1, m + 1, rb, x, k);
	tr[rt] = max(tr[rt << 1], tr[rt << 1 | 1]);
}

int query(int rt, int lb, int rb, int l, int r){
	int m = lb + rb >> 1;
	if(lb == l && r == rb)
		return tr[rt];
	if(r <= m)
		return query(rt << 1, lb, m, l, r);
	if(l > m)
		return query(rt << 1 | 1, m + 1, rb, l, r);
	return max(query(rt << 1, lb, m, l, m), query(rt << 1 | 1, m + 1, rb, m + 1, r));
}

void dfs(int u, int par, int depth){
	vis[u] = sz[u] = 1;
	fa[u] = par;
	dep[u] = depth;
	mxson[u] = -1;
	for(pii i : v[u])
		if(!vis[i.F]){
			dfs(i.F, u, depth + 1);
			sz[u] += sz[i.F];
			if(!~mxson[u] || sz[i.F] > sz[mxson[u]])
				mxson[u] = i.F;
		}
}

void dfs2(int u, int top){
	vis[u] = 1;
	lt[u] = top;
	idx[u] = inc++;
	if(!~mxson[u])
		return;
	dfs2(mxson[u], top);
	for(pii i : v[u]){
		if(!vis[i.F]){
			dfs2(i.F, i.F);
			modify(1, 1, n, idx[i.F], i.S);
		}
		if(i.F == mxson[u])
			modify(1, 1, n, idx[i.F], i.S);
	}
}

int lcamx(int a, int b){
	int mx = 0;
	while(lt[a] != lt[b]){
		if(dep[a] > dep[b])
			swap(a, b);
		if(b == lt[b])
			mx = max(mx, query(1, 1, n, idx[b], idx[b]));
		else
			mx = max(mx, query(1, 1, n, idx[mxson[lt[b]]], idx[b]));
		b = fa[lt[b]];
	}
	if(a == b)
		return mx;
	if(dep[a] < dep[b])
		return max(mx, query(1, 1, n, idx[mxson[a]], idx[b]));
	return max(mx, query(1, 1, n, idx[mxson[b]], idx[a]));
}

int main() {
	int m, c;
	ll ans = 0;
	cin >> n >> m;
	for(int i = 0; i < m; i++)
		cin >> a[i].u >> a[i].v >> a[i].w;
	sort(a, a + m);
	c = n;
	for(int i = 1; i <= n; i++)
		boss[i] = i;
	for(int i = 0; c > 1 && i < m; i++){
		if(find(a[i].u) == find(a[i].v))
			continue;
		combine(a[i].u, a[i].v);
		edges.pb(a[i]);
		used[i] = 1;
		c--;
	}
	c = n;
	for(int i = 1; i <= n; i++)
		boss[i] = i;
	for(int i = 0; c > 1 && i < m; i++){
		if(find(a[i].u) == find(a[i].v) || used[i])
			continue;
		combine(a[i].u, a[i].v);
		v[a[i].u].pb(MP(a[i].v, a[i].w));
		v[a[i].v].pb(MP(a[i].u, a[i].w));
		c--;
	}
	if(c > 1)
		return cout << "-1\n", 0;
	dfs(1, 1, 1);
	vis.reset();
	dfs2(1, 1);
	for(edge i : edges)
		ans += lcamx(i.u, i.v) + 1 - i.w;
	cout << ans << "\n";
}