#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using VI = vector<ll>;
using VV = vector<VI>;
using VS = vector<string>;
using PII = pair<ll, ll>;

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define rep(i,b) FOR(i, 0, b)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<'\n'
#define p2(s, t) cout << (s) << " " << (t) << '\n'
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << '\n'
#define SZ(x) ((int)(x).size())
#define MP make_pair

const ll mod = 1e9 + 7;
const ll inf = 1e18;
const double PI = acos(-1);

struct Edge{
    ll to;
    ll cost;
    Edge(ll to, ll cost): to(to), cost(cost) {}
};

ll ans = 0;
ll N; 
vector<vector<Edge>> G;
map<PII, ll> mp; // i, j間のedgeコスト(キーはi<jとする)

// 距離（遅いVER・ナイーブ）
ll dist(ll i, ll j){
  for(auto edge : G[i]){
    if(edge.to==j) return edge.cost;
  }
  return -1;
}

ll dist2(ll i, ll j){
  if(i>j){
    swap(i, j);
  }
  return mp[MP(i, j)];
}

// i以降のノード数を返す
// (iも含む)
ll dfs(ll i, ll prev){
  ll sum = 0;
  for(auto edge : G[i]){
    if(edge.to==prev) continue;
    sum += dfs(edge.to, i);
  }

  ll a = sum+1;
  ll b = N-a;
  ll d = dist2(i, prev);
  ans += a*b*d;

  return sum+1;
}

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

    // input
    cin >> N;
    G.resize(N);

    rep(i, N-1){
      ll u, v, w;
      cin >> u >> v >> w;
      u--; v--;
      G[u].push_back(Edge(v, w));
      G[v].push_back(Edge(u, w));

      if(u<v){
        mp[MP(u, v)] = w;
      }else{
        mp[MP(v, u)] = w;
      }
    }

    dfs(0, -1);
    p(ans*2);
    
    return 0;
}