#include <bits/stdc++.h>
#define cinf(n,x) for(int i=0;i<(n);i++)cin>>x[i];
#define ft first
#define sc second
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define all(v) (v).begin(),(v).end()
#define LB(a,x) lb(all(a),x)-a.begin()
#define UB(a,x) ub(all(a),x)-a.begin()
#define mod 1000000007
#define FS fixed<<setprecision(15)
using namespace std;
typedef long long ll;
#define rep(i,n) for(ll i=0;i<n;i++)
const double pi=3.141592653589793;
template<class T> using V=vector<T>;
using Graph = vector<vector<int>>;
using P=pair<ll,ll>;
typedef unsigned long long ull;
typedef long double ldouble;
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }

const ll INF=1e18;

V<ll> cnt;
V<ll> par;
V<V<ll>> G;

void dfs(ll v,ll p){
    for(ll u:G[v]){
        if(u==p) continue;
        dfs(u,v);
        cnt[v]+=cnt[u];
    }
    cnt[v]++;
    par[v]=p;
}

struct edge{
    ll to;
    ll cost;
};

int main(){
    cin.tie(0);ios::sync_with_stdio(false);
    ll n;
    cin>>n;
    cnt.resize(n);
    G.resize(n);
    par.resize(n);
    map<P,ll> mp;
    rep(i,n-1){
        ll u,v,w;
        cin>>u>>v>>w;
        u--;v--;
        G[u].push_back(v);
        G[v].push_back(u);
        mp[P(u,v)]=mp[P(v,u)]=w;
    }
    dfs(0,-1);
    ll ans=0;
    rep(i,n){
        if(cnt[i]==n) continue;
        ll v=par[i];
        ans+=2*cnt[i]*(n-cnt[i])*mp[P(i,v)];
    }
    cout<<ans<<endl;
}