#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)

vector<pair<int, int > > g[200000];
int n;
long long ret;

int dfs(int v, int par = -1) {
  int sub = 1; // me
  for (auto &pr: g[v]) {
    int u = pr.first;
    int w = pr.second;
    if (u == par)
      continue;
    int tmp = dfs(u, v);
    ret += (long long)tmp * (n - tmp) * w;
    sub += tmp;
  }
  return sub;
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  cin >> 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);
  }
  ret = 0;
  dfs(0);
  cout << 2 * ret << endl;
  
  return 0;
}