#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using P = pair<int, ll>;

ll solve(int cur, int par, vector< vector<P> >& g, ll& ans) {
    ll n = g.size();

    ll res = 1;
    for (P& e : g[cur]) {
        if (e.first == par) continue;
        ll num = solve(e.first, cur, g, ans);
        res += num;
        ans += e.second * num * (n - num) * 2;
    }
    return res;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    vector< vector<P> > g(n);
    for (int i = 1; i < n; i++) {
        int u, v;
        ll w;
        cin >> u >> v >> w;
        u--; v--;
        g[u].emplace_back(v, w);
        g[v].emplace_back(u, w);
    }

    ll ans = 0;
    solve(0, -1, g, ans);
    cout << ans << endl;
    return 0;
}