#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

ll r = 0;

struct Graph {
    struct Vertex { int n, k; ll s; };
    struct Edge { int i, n, c; };
    Graph(int n, int m) : v(n, { -1, 0, 0 }), e(m), n(n), m(0) {}
    void add_edge(int i, int j, int c) {
        e[m] = { j, v[i].n, c };
        v[i].n = m;
        m++;
    }
    pair<ll, int> dfs(int i, int c, int p) {
        ll s = c;
        int k = 1;
        for (int j = v[i].n; j >= 0; j = e[j].n) {
            Edge &o = e[j];
            if (o.i == p) continue;
            auto p = dfs(o.i, c + o.c, i);
            s += p.first;
            k += p.second;
        }
        return { v[i].s = s, v[i].k = k };
    }
    void dfs2(int i, int c, ll s, int p) {
        ll t = (v[i].s - (ll)c * v[i].k) + s;
        r += t;
        for (int j = v[i].n; j >= 0; j = e[j].n) {
            Edge &o = e[j];
            if (o.i == p) continue;
            dfs2(o.i, c + o.c, t - (v[o.i].s - (ll)c * v[o.i].k) + (ll)o.c * (n - v[o.i].k), i);
        }
    }
    vector<Vertex> v;
    vector<Edge> e;
    int n, m;
};

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n;
    cin >> n;

    Graph g(n, (n - 1) * 2);
    for (int i = 0; i < n - 1; i++) {
        int a, b, c;
        cin >> a >> b >> c;
        a--; b--;

        g.add_edge(a, b, c);
        g.add_edge(b, a, c);
    }

    g.dfs(0, 0, -1);
    g.dfs2(0, 0, 0, -1);

    cout << r << endl;

    return 0;
}