#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define P pair<ll,ll>
#define FOR(I,A,B) for(ll I = ll(A); I < ll(B); ++I)
#define FORR(I,A,B) for(ll I = ll((B)-1); I >= ll(A); --I)
#define TO(x,t,f) ((x)?(t):(f))
#define SORT(x) (sort(x.begin(),x.end())) // 0 2 2 3 4 5 8 9
#define POSL(x,v) (lower_bound(x.begin(),x.end(),v)-x.begin()) //xi>=v  x is sorted
#define POSU(x,v) (upper_bound(x.begin(),x.end(),v)-x.begin()) //xi>v  x is sorted
#define NUM(x,v) (POSU(x,v)-POSL(x,v))  //x is sorted
#define REV(x) (reverse(x.begin(),x.end())) //reverse
ll gcd(ll a,ll b){if(a%b==0)return b;return gcd(b,a%b);}
ll lcm(ll a,ll b){ll c=gcd(a,b);return ((a/c)*(b/c)*c);}
#define NEXTP(x) next_permutation(x.begin(),x.end())
const ll INF=ll(1e18)+ll(7);
const ll MOD=1000000007LL;
#define out(a) cout<<fixed<<setprecision((a))

vector<ll> tree[200003];
ll ans = 0;
ll N;
ll root = 1;
ll pa[200009]={};
ll numch[200009]={};
bool did[200009];
vector<ll> U,V,W;

void dfs(int i = 1){
	did[i] = true;
	for(auto ch:tree[i]){
		if(did[ch])continue;
		pa[ch] = i;
		dfs(ch);
	}
}

int main(){
	cin >> N;
	FOR(i,0,N-1){
		ll u,v,w;
		cin >> u >> v >> w;
		tree[u].push_back(v);
		tree[v].push_back(u);
		U.push_back(u);
		V.push_back(v);
		W.push_back(w);
	}
	dfs();
	FOR(i,1,N+1) did[i] = false;
	vector<ll> dodo;
	queue<ll> q;
	q.push(1);
	did[1] = true;
	while(q.size()){
		ll ind = q.front();
		q.pop();
		dodo.push_back(ind);
		for(auto nex:tree[ind]){
			if(not did[nex]){
				did[nex] = true;
				q.push(nex);
			}
		}
	}
	reverse(dodo.begin(), dodo.end());
	//cout << dodo.size() << endl;
	ll cnt[N+1] = {};
	FOR(i,0,N+1)cnt[i]=1;
	for(auto x:dodo){
		cnt[pa[x]]+=cnt[x];
	}
	FOR(i,0,N-1){
		ll chai;
		if(pa[U[i]]==V[i]){
			chai = U[i];
		}else{
			chai = V[i];
		}
		ans += W[i] * cnt[chai] * (N-cnt[chai]);
	}
	cout << ans*2 << endl;
}