#include <bits/stdc++.h>
#define rep(i, n) for(int(i) = 0; (i) < (n); (i)++)
#define FOR(i, m, n) for(int(i) = (m); (i) < (n); (i)++)
#define ALL(v) (v).begin(), (v).end()
#define LLA(v) (v).rbegin(), (v).rend()
#define SZ(v) (v).size()
#define INT(...)                                                               \
    int __VA_ARGS__;                                                           \
    read(__VA_ARGS__)
#define LL(...)                                                                \
    ll __VA_ARGS__;                                                            \
    read(__VA_ARGS__)
#define DOUBLE(...)                                                            \
    double __VA_ARGS__;                                                        \
    read(__VA_ARGS__)
#define CHAR(...)                                                              \
    char __VA_ARGS__;                                                          \
    read(__VA_ARGS__)
#define STRING(...)                                                            \
    string __VA_ARGS__;                                                        \
    read(__VA_ARGS__)
#define VEC(type, name, size)                                                  \
    vector<type> name(size);                                                   \
    read(name)
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using Graph = vector<vector<int>>;
template <typename T> struct edge {
    int to;
    T cost;
    edge(int t, T c) : to(t), cost(c) {}
};
template <typename T> using WGraph = vector<vector<edge<T>>>;
const int INF = 1 << 30;
const ll LINF = 1LL << 60;
const int MOD = 1e9 + 7;
template <class T> inline vector<T> make_vec(size_t a, T val) {
    return vector<T>(a, val);
}
template <class... Ts> inline auto make_vec(size_t a, Ts... ts) {
    return vector<decltype(make_vec(ts...))>(a, make_vec(ts...));
}

void read() {}
template <class T> inline void read(T &a) { cin >> a; }
template <class T, class S> inline void read(pair<T, S> &p) {
    read(p.first), read(p.second);
}
template <class T> inline void read(vector<T> &v) {
    for(auto &a : v)
        read(a);
}
template <class Head, class... Tail>
inline void read(Head &head, Tail &...tail) {
    read(head), read(tail...);
}
template <class T> inline void chmax(T &a, T b) { (a < b ? a = b : a); }
template <class T> inline void chmin(T &a, T b) { (a > b ? a = b : a); }

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    INT(n);
    WGraph<ll> g(n);
    vector<edge<ll>> edges;
    rep(i, n - 1) {
        INT(u, v, w);
        u--, v--;
        g[u].emplace_back(v, w);
        g[v].emplace_back(u, w);
    }
    vector<int> sz(n);
    vector<int> order(n);
    int ord = 0;
    auto dfs = [&](auto &&dfs, int v, int p) -> int {
        if(sz[v] != 0)
            return sz[v];
        int ret = 1;
        order[v] = ord++;
        for(auto c : g[v]) {
            if(c.to == p)
                continue;
            ret += dfs(dfs, c.to, v);
        }
        return sz[v] = ret;
    };
    dfs(dfs, 0, -1);
    ll res = 0;
    for(int i = 0; i < n; i++) {
        for(auto e : g[i]) {
            int v = i, c = e.to;
            if(order[v] > order[c])
                swap(v, c);
            res += e.cost * sz[c] * (n - sz[c]);
        }
    }
    cout << res << endl;
}