#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; (i) < (int)(n); ++ (i))
#define ALL(x) begin(x), end(x)
using ll = long long;
using namespace std;

int main() {
    // input
    int n; cin >> n;
    vector<vector<pair<int, ll> > > g(n);
    REP (i, n - 1) {
        int u, v, w; cin >> u >> v >> w;
        -- u;
        -- v;
        g[u].emplace_back(v, w);
        g[v].emplace_back(u, w);
    }

    // solve
    ll d = 0;
    function<int (int, int)> go = [&](int i, int parent) -> int {
        vector<int> sizes;
        for (auto edge : g[i]) {
            int j, cost; tie(j, cost) = edge;
            if (j == parent) continue;
            int size = go(j, i);
            sizes.push_back(size);
            d += 2ll * size * (n - size) * cost;
        }
        return accumulate(ALL(sizes), 0) + 1;
    };
    go(0, -1);

    // output
    cout << d << endl;
    return 0;
}