#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include <algorithm>
#include <cmath>
#include <queue>
#include <map>
#include <set>
#include <cstdlib>
#include <bitset>
#include <tuple>
#include <assert.h>
#include <deque>
#include <bitset>
#include <iomanip>
#include <limits>
#include <chrono>
#include <random>
#include <array>
#include <unordered_map>
#include <functional>
#include <complex>

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

const long long MAX = 5100000;
const long long INF = 1LL << 60;
const long long mod = 1000000007LL;
//const long long mod = 998244353LL;

using namespace std;
typedef unsigned long long ull;
typedef long long ll;

ll N;
vector<vector<int>> g;
vector<ll> cnt;
vector<ll> h;

void dfs1(ll cur, ll pre) {
	for (auto next : g[cur]) {
		if (next == pre) continue;
		h[next] = h[cur] + 1;
		dfs1(next, cur);
	}
}

ll dfs2(ll cur, ll pre) {
	ll res = 1;
	for (auto next : g[cur]) {
		if (next == pre) continue;
		res += dfs2(next, cur);
	}
	return cnt[cur] = res;
}

class Edge {
public:
	ll source, target, cost;
	Edge(ll source = 0, ll target = 0, ll cost = 0) :
		source(source), target(target), cost(cost) {}
	bool operator<(const Edge &e)const {
		return cost < e.cost;
	}
};

int main()
{
	/*
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	*/
	scanf("%lld", &N);
	g.resize(N);
	cnt = vector<ll>(N);
	h = vector<ll>(N);
	vector<Edge> edges;
	for (ll i = 0; i < N - 1; i++) {
		ll u, v, w; scanf("%lld %lld %lld", &u, &v, &w);
		u--; v--;
		if (u > v) swap(u, v);
		g[u].emplace_back(v);
		g[v].emplace_back(u);
		edges.emplace_back(u, v, w);
	}
	dfs1(0, -1);
	dfs2(0, -1);
	ll res = 0;
	for (auto p : edges) {
		ll u = p.source;
		ll v = p.target;
		if (h[u] > h[v]) swap(u, v);
		res += cnt[v] * (N - cnt[v]) * p.cost * 2;
	}
	cout << res << endl;
	return 0;
}