#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
typedef pair<ll, P> P3;
typedef pair<P, P> PP;
constexpr ll MOD = ll(1e9 + 7);
constexpr int IINF = INT_MAX;
constexpr ll LLINF = LLONG_MAX;
constexpr int MAX_N = int(1e5) + 5;
constexpr double EPS = 1e-9;
constexpr int di[] = {0, 1, 0, -1}, dj[] = {1, 0, -1, 0};
#define REP(i, n) for (int i = 0; i < n; i++)
#define REPR(i, n) for (int i = n; i >= 0; i--)
#define SORT(v) sort((v).begin(), (v).end())
#define SORTR(v) sort((v).rbegin(), (v).rend())
#define ALL(v) (v).begin(), (v).end()

vector<vector<P> > g;
ll n;
ll ans = 0;

ll dfs(int v, int p){
    ll res = 0;
    for(auto e : g[v]){
        int u = e.first;
        if(u == p) continue;
        ll cnt = dfs(u, v);
        ans += cnt*(n-cnt)*e.second;
        res += cnt;
    }
    return res+1;
}


int main() {
    cin >> n;
    g.resize(n);
    for(int i=0;i<n-1;i++){
        ll u, v, w;
        cin >> u >> v >> w;
        u--; v--;
        g[u].push_back({v, w});
        g[v].push_back({u, w});
    }
    dfs(0,-1);
    cout << ans*2 << endl;
    return 0;
}