#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
long long ans = 0;
int n;
vector<pair<int, int>> g[202020];
int dfs (int cur, int par) {
  int res = 0;
  for (auto nxt : g[cur]) {
    if (nxt.first == par) continue;
    int x = dfs(nxt.first, cur);
    res += x;
    ans += 1LL * x * (n - x) * nxt.second;
  }
  return res + 1;
}
signed main() {
  ios::sync_with_stdio(false); cin.tie(0);
  cin >> n;
  for (int i = 1; i < n; i++) {
    int u, v, w;
    cin >> u >> v >> w;
    u--;
    v--;
    g[u].emplace_back(v, w);
    g[v].emplace_back(u, w);
  }
  dfs(0, -1);
  cout << ans * 2 << endl;
  return 0;
}