#include <bits/stdc++.h>
using namespace std;
using lint = long long;
template<class T = int> using V = vector<T>;
template<class T = int> using VV = V< V<T> >;

int main() {
  cin.tie(nullptr); ios::sync_with_stdio(false);
  int n; cin >> n;
  struct Edge { int to, w; };
  VV<Edge> g(n);
  for (int _ = 0; _ < n - 1; ++_) {
    int u, v, w; cin >> u >> v >> w, --u, --v;
    g[u].emplace_back(Edge{v, w});
    g[v].emplace_back(Edge{u, w});
  }
  lint res = 0;
  V<> sz(n);
  auto dfs = [&](const auto& dfs, int v, int p) -> void {
    sz[v] = 1;
    for (const auto& e : g[v]) if (e.to != p) {
      dfs(dfs, e.to, v);
      res += sz[e.to] * (n - sz[e.to]) * e.w;
      sz[v] += sz[e.to];
    }
  };
  dfs(dfs, 0, -1);
  cout << 2 * res << '\n';
}