#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <algorithm>
#include <set>
#include <map>
#include <bitset>
#include <cmath>
#include <functional>
#include <iomanip>
#define vll vector<ll>
#define vvvl vector<vvl>
#define vvl vector<vector<ll>>
#define VV(a, b, c, d) vector<vector<d>>(a, vector<d>(b, c))
#define VVV(a, b, c, d) vector<vvl>(a, vvl(b, vll (c, d)));
#define re(c, b) for(ll c=0;c<b;c++)
#define rep(a,b,c) for(ll a=b;a<c;a++)
#define all(obj) (obj).begin(), (obj).end()
typedef long long int ll;
typedef long double ld;
using namespace std;

void get(vll &a){re(i,a.size()) scanf("%lld",&a[i]);}
void get(vvl &a){re(i,a.size()) re(j,a[0].size()) scanf("%lld",&a[i][j]);}
void print(vll &a){re(i,a.size()) cout<<a[i]<<(i==a.size()-1?"\n":" ");}
void print(vvl &a){re(i,a.size()) re(j,a[0].size())cout<<a[i][j]<<(j==a[0].size()-1?"\n":" ");}

struct edge{
  ll to, w;
};
vector<vector<edge>> G(200001, vector<edge>());
vll dist(200001, 0);
vll c(200001, 0);
vll ans(200001, 0);

map<ll, ll> mp;
void f(ll now, ll from){
  vvl p;
  for(auto e:G[now]){
    if(e.to==from) continue;
    f(e.to, now);
    //子の数だけ
    p.push_back({dist[e.to] + c[e.to]*e.w, c[e.to]});
    ans[now] += dist[e.to] + c[e.to]*e.w;
    dist[now] += dist[e.to] + c[e.to]*e.w;
    c[now] += c[e.to];
  }
  for(int i=0;i<p.size();i++){
    for(int j=i+1;j<p.size();j++){
      ans[now] += p[i][0] * p[j][1];
      ans[now] += p[j][0] * p[i][1];
    }
  }
  c[now]++;
}
int main(int argc, char const *argv[]) {
  ll n;std::cin >> n;
  re(i, n-1){
    ll a, b, c;std::cin >> a >> b >> c;
    G[a].push_back({b, c});
    G[b].push_back({a, c});
  }
  f(1, -1);
  ll s = 0;
  for(int i=1;i<=n;i++) s += ans[i];
  std::cout << s*2 << '\n';
}