#include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < (n); i++)
#define repr(i, n) for (int i = (n) - 1; i >= 0; i--)
#define range(a) a.begin(), a.end()

using namespace std;
using ll = long long;

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(15);
  int N; cin >> N;
  vector<vector<pair<ll, ll>>> G(N);
  rep(i, N - 1) {
    int a, b, c; cin >> a >> b >> c; a--; b--;
    G[a].emplace_back(b, c);
    G[b].emplace_back(a, c);
  }
  vector<int> size(N);
  ll ans = 0;
  auto dfs = [&](auto dfs, int u, int p) -> void {
    size[u]++;
    for (auto e : G[u]) if (e.first != p) {
      dfs(dfs, e.first, u);
      size[u] += size[e.first];
    }
    for (auto e : G[u]) if (e.first != p) {
      ans += (ll)e.second * size[e.first] * (N - size[e.first]);
    }
  };
  dfs(dfs, 0, -1);
  cout << ans*2 << endl;
}