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

#define ALL(obj) (obj).begin(),(obj).end()
#define SPEED cin.tie(0);ios::sync_with_stdio(false);

template<class Operator> class Tree {
	Operator Op;                            
	using typeDist = decltype(Op.unitDist); 
	size_t num;
	size_t ord;
public:
	vector<vector<pair<size_t,typeDist>>> edge;
	vector<size_t> depth;
	vector<size_t> order;
	vector<typeDist> dist;
	vector<pair<size_t,typeDist>> parent;
	vector<vector<pair<size_t,typeDist>>> child;
	vector<array<pair<size_t,typeDist>,Operator::bit>> ancestor;
	vector<size_t> size;
	vector<vector<size_t>> descendant;
	Tree(const int num):num(num),edge(num),depth(num,-1),order(num),dist(num){}
	//O(1) anytime
	void makeEdge(const int& from, const int& to, const typeDist w = 1) {
		edge[from].push_back({to,w});
	}
	//O(N) anytime
	void makeDepth(const int root) {
		depth[root] = 0;
		dist[root] = Op.unitDist;
		ord = 0;
		dfs1(root);
		order[ord++] = root;
	}
	//O(N) anytime
	void makeDepth(void) {
		ord = 0;
		for(size_t root = 0; root < num; ++root) {
			if(depth[root] != -1) continue;
			depth[root] = 0;
			dist[root] = Op.unitDist;
			dfs1(root);
			order[ord++] = root;
		}
	}
	//for makeDepth
	void dfs1(int curr, int prev = -1){
		for(auto& e:edge[curr]){
			int next = e.first;
			if(next==prev) continue;
			depth[next] = depth[curr] + 1;
			dist[next]  = Op.funcDist(dist[curr],e.second);
			dfs1(next,curr);
			order[ord++] = next;
		}
	}
	//O(N) after makeDepth
	void makeParent(void) {
		parent.resize(num,make_pair(num,Op.unitDist));
		for (size_t i = 0; i < num; ++i) for (auto& e : edge[i]) if (depth[i] > depth[e.first]) parent[i] = e;
	}
	//O(N) after makeDepth
	void makeChild(void) {
		child.resize(num);
		for (size_t i = 0; i < num; ++i) for (auto& e : edge[i]) if (depth[i] < depth[e.first]) child[i].push_back(e);
	}
	//O(NlogN) after makeDepth and makeParent
	void makeAncestor(void) {
		ancestor.resize(num);
		for (size_t i = 0; i < num; ++i) ancestor[i][0] = (parent[i].first!=num?parent[i]:make_pair(i,Op.unitLca));
		for (size_t j = 1; j < Operator::bit; ++j) {
			for (size_t i = 0; i < num; ++i) {
				size_t k = ancestor[i][j - 1].first;
				ancestor[i][j] = Op.funcLca(ancestor[k][j - 1],ancestor[i][j - 1]);
			}
		}
	}
	//O(logN) after makeAncestor
	//return {lca,lca_dist} l and r must be connected
	pair<size_t,typeDist> lca(size_t l, size_t r) {
		if (depth[l] < depth[r]) swap(l, r);
		int diff = depth[l] - depth[r];
		auto ancl = make_pair(l,Op.unitLca);
		auto ancr = make_pair(r,Op.unitLca);
		for (int j = 0; j < Operator::bit; ++j) {
			if (diff & (1 << j)) {
				ancl = Op.funcLca(ancestor[ancl.first][j],ancl);
			}
		}
		if(ancl.first==ancr.first) return ancl;
		for (int j = Operator::bit - 1; 0 <= j; --j) {
			if(ancestor[ancl.first][j].first!=ancestor[ancr.first][j].first) {
				ancl = Op.funcLca(ancestor[ancl.first][j],ancl);
				ancr = Op.funcLca(ancestor[ancr.first][j],ancr);
			}
		}
		ancl = Op.funcLca(ancestor[ancl.first][0],ancl);
		ancr = Op.funcLca(ancestor[ancr.first][0],ancr);
		return Op.funcLca(ancl,ancr);
	}
	//O(N) anytime
	int diameter(void){
		makeDepth(0);
		int tmp = max_element(depth.begin(), depth.end()) - depth.begin();
		makeDepth(tmp);
		return *max_element(depth.begin(), depth.end());
	}
	//O(N^2) after makeDepth (include self)
	void makeDescendant(void) {
		descendant.resize(num);
		for (size_t i = 0; i < num; ++i) descendant[i].push_back(i);
		for (size_t i = 0; i < num; ++i) for (auto& e : edge[order[i]]) if (depth[order[i]] < depth[e.first]) for(auto k: descendant[e.first]) descendant[order[i]].push_back(k);
	}
	//O(N) after makeChild
	void makeSize(void) {
		size.resize(num,1);
		for (size_t i:order) for (auto e : child[i]) size[i] += size[e.first];
	}
};
template<class typeDist> struct treeOperator{
	static const size_t bit = 20;
	typeDist unitDist = 0;
	typeDist unitLca = 0;
	typeDist funcDist(const typeDist& parent,const typeDist& w){return parent+w;}
	pair<size_t,typeDist> funcLca(const pair<size_t,typeDist>& l,const pair<size_t,typeDist>& r){return make_pair(l.first,max(l.second,r.second));}
};
 
//depth,dist
//https://atcoder.jp/contests/abc126/tasks/abc126_d
//child
//https://atcoder.jp/contests/abc133/tasks/abc133_e
//lca
//https://atcoder.jp/contests/abc014/tasks/abc014_4
//weighted lca
//https://atcoder.jp/contests/code-thanks-festival-2017-open/tasks/code_thanks_festival_2017_h
//https://atcoder.jp/contests/cf16-tournament-round1-open/tasks/asaporo_c
//diameter
//https://atcoder.jp/contests/agc033/tasks/agc033_c
//descendant
//https://atcoder.jp/contests/code-thanks-festival-2018/tasks/code_thanks_festival_2018_f
//size
//
//eulerTour
//https://yukicoder.me/problems/no/900

// Tree<treeOperator<int>> tree(N);

int main() {
	int N;
	cin >> N;
	Tree<treeOperator<ll>> tree(N);
	for(int i = 0; i < N-1; ++i){
		int u,v,w;
		cin >> u >> v >> w;
		u--,v--;
		tree.makeEdge(u,v,w);
		tree.makeEdge(v,u,w);
	}
	tree.makeDepth(0);
	tree.makeChild();
	tree.makeSize();
	ll ans = 0;
	for(int pa:tree.order) for(auto e:tree.child[pa]) ans += e.second*tree.size[e.first]*(N-tree.size[e.first])*2LL;
	cout << ans << endl;
    return 0;	return 0;
}