#include <cstdio>
#include <iostream>
#include <algorithm>
#include <vector>
#include <map>

using std::cin;
using std::cout;

using i64 = long long;
using pii = std::pair<int, int>;

const int nx = 1e5;
const int mx = 2e5;

int n;

int m;
struct edge {
    int u, v, w;
}ed[mx + 5], ed1[mx + 5];

int siz[nx + 5];
int fa[nx + 5];

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

int vis[mx + 5];
bool done[mx + 5];
std::vector<int> qv[nx + 5];

int main() {
    std::ios::sync_with_stdio(false);

    cin >> n >> m;
    for (int i = 1; i <= m; ++i)
        cin >> ed[i].u >> ed[i].v >> ed[i].w;
    std::sort(ed + 1, ed + m + 1, [](edge x, edge y) {
        return x.w < y.w;
    });

    for (int i = 1; i <= n; ++i) fa[i] = i, siz[i] = 1;

    for (int i = 1; i <= m; ++i) {
        int fu = find(ed[i].u), fv = find(ed[i].v);
        if (fu == fv) continue;
        if (siz[fu] < siz[fv]) std::swap(fu, fv);
        siz[fu] += siz[fv], fa[fv] = fu;
        vis[i] = 1;
    }
    
    for (int i = 1; i <= n; ++i) fa[i] = i, siz[i] = 1;
    for (int i = 1; i <= m; ++i) {
        if (vis[i] == 1) {
            qv[ed[i].u].emplace_back(i);
            qv[ed[i].v].emplace_back(i);
        }
    }
    i64 ans = 0;
    for (int i = 1; i <= m; ++i) if (vis[i] != 1) {
        int fu = find(ed[i].u), fv = find(ed[i].v);
        if (fu == fv) continue;
        if (siz[fu] < siz[fv]) std::swap(fu, fv);
        for (int qi : qv[fv]) {
            if (done[qi]) continue;
            int tu = find(ed[qi].u), tv = find(ed[qi].v);
            if (siz[tu] < siz[tv]) std::swap(tu, tv);
            if (tv == fv && tu == fu) {
                done[qi] = true;
                ans += std::max(ed[i].w + 1 - ed[qi].w, 0);
            }else qv[fu].emplace_back(qi);
        }
        siz[fu] += siz[fv];
        fa[fv] = fu;
    }
    if (siz[find(1)] != n) cout << "-1\n";
    else cout << ans << '\n';
    return 0;
}