#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>
#define LP pair<ll, ll>

template<class T>
void chmax(T& a, T b) { a = max(a, b); };
template<class T>
void chmin(T& a, T b) { a = min(a, b); };

struct Edge {
  int to, c;
  Edge(int to, int c) : to(to), c(c) {}
};

int n;
vector<Edge> G[200005];
int dp[200005];

void dfs(int v, int p=-1) {
  dp[v] = 1;
  for (auto e : G[v]) {
    if (e.to == p) continue;
    dfs(e.to, v);
    dp[v] += dp[e.to];
  }
}

ll ans = 0;
void dfs2(int v, int p=-1) {
  for (auto e : G[v]) {
    if (e.to == p) continue;
    ans += (ll)e.c*dp[e.to]*(n-dp[e.to]);
    dfs2(e.to, v);
  }


}

int main() {
  cin >> n;
  rep(i,n-1) {
    int u, v, w;
    cin >> u >> v >> w;
    u--, v--;
    G[u].push_back(Edge(v,w));
    G[v].push_back(Edge(u,w));
  }
  dfs(0);

  dfs2(0);
  ans *= 2;
  cout << ans << endl;




  return 0;
}