#include <bits/stdc++.h>
using namespace std;
void dfs(vector<int> &dp, vector<vector<pair<int, int>>> &c, int v = 0){
  dp[v] = 1;
  for (auto P : c[v]){
    int w = P.second;
    dfs(dp, c, w);
    dp[v] += dp[w];
  }
}
int main(){
  int N;
  cin >> N;
  vector<vector<pair<int, int>>> E(N);
  for (int i = 0; i < N - 1; i++){
    int u, v, w;
    cin >> u >> v >> w;
    u--;
    v--;
    E[u].push_back(make_pair(w, v));
    E[v].push_back(make_pair(w, u));
  }
  vector<int> p(N, -1);
  vector<vector<pair<int, int>>> c(N);
  queue<int> Q;
  Q.push(0);
  while (!Q.empty()){
    int v = Q.front();
    Q.pop();
    for (auto P : E[v]){
      int w = P.second;
      if (w != p[v]){
        p[w] = v;
        c[v].push_back(P);
        Q.push(w);
      }
    }
  }
  vector<int> dp(N);
  dfs(dp, c);
  long long ans = 0;
  for (int i = 0; i < N; i++){
    for (auto P : c[i]){
      int d = P.first;
      int s = P.second;
      ans += (long long) d * dp[s] * (N - dp[s]);
    }
  }
  ans *= 2;
  cout << ans << endl;
}