#include <bits/stdc++.h>
#define REP(i, start, end) for (int i=start, i##Len=(end); i < i##Len; ++i)
using ll = int64_t;
using namespace std;

int N;
vector<vector<pair<ll, ll>>> tree;
int counts[200010] = {};

int rec(int v, int parent) {
    counts[v] = 1;
    for (auto p: tree[v]) {
        if (p.first == parent) continue;
        counts[v] += rec(p.first, v);
    }
    return counts[v];
}

ll solve(int v, int parent) {
    ll total = 0;
    for (auto p : tree[v]) {
        if (p.first == parent) continue;
        total += p.second * counts[p.first] * (N-counts[p.first]) * 2 + solve(p.first, v);
    }
    return total;
}


int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);

    cin >> N;
    tree = vector<vector<pair<ll, ll>>>(N+1);

    ll u, v, w;
    REP(i, 0, N-1) {
        cin >> u >> v >> w;
        tree[u].emplace_back(v, w);
        tree[v].emplace_back(u, w);
    }

    rec(1, 0);
    cout << solve(1, 0) << endl;

    return 0;
}