#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;
using Edge = pair<int,int>;
using Graph = vector<vector<Edge>>;

Graph G;
ll res = 0;
ll dfs(int u, int p, ll n){
  ll c = 0;
  for (auto v : G[u]) {
    if (v.first == p) continue;
    ll d = dfs(v.first, u, n);
    res += v.second * d * (n - d);
    c += d;
  }
  return c + 1;
}

int main(){
  int n;
  cin >> n;
  G.resize(n);

  rep(i,n-1){
    int u, v, w;
    cin >> u >> v >> w;
    u--; v--;
    G[u].push_back({v,w});
    G[v].push_back({u,w});
  }
  dfs(0,-1,n);
  cout << res * 2<< endl;
  return 0;
}