#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <limits.h>
#include <map>
#include <queue>
#include <set>
#include <string.h>
#include <vector>

using namespace std;
typedef long long ll;

const int MAX_N = 200010;

struct Edge {
  int v;
  ll w;

  Edge(int v = -1, ll w = -1) {
    this->v = v;
    this->w = w;
  }
};

vector<Edge> E[MAX_N];
vector<int> V[MAX_N];
ll ans;
int N;

int dfs1(int u, int parent = -1) {
  int cnt = 0;

  for (Edge &e : E[u]) {
    if (e.v == parent) continue;

    int v_cnt = dfs1(e.v, u);
    cnt += v_cnt;
    V[u].push_back(v_cnt);
  }

  return cnt + 1;
}

void dfs2(int u, int v_cnt = 0, int parent = -1) {
  int t_cnt = v_cnt;
  for (int c : V[u]) {
    t_cnt += c;
  }

  int i = 0;

  for (Edge &e : E[u]) {
    if (e.v == parent) continue;

    int cnt = V[u][i];
    ans += 2 * e.w * (N - cnt) * cnt;
    dfs2(e.v, t_cnt - cnt + 1, u);
    i += 1;
  }
}

int main() {
  cin >> N;

  int u, v;
  ll w;
  for (int i = 0; i < N - 1; ++i) {
    cin >> u >> v >> w;

    E[u].push_back(Edge(v, w));
    E[v].push_back(Edge(u, w));
  }

  ans = 0;
  dfs1(1);
  dfs2(1);

  cout << ans << endl;

  return 0;
}