#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 <fstream>
#include <bitset>
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 INF = 1LL << 60;
const long long MOD = 1000000007LL;
const long long MAX = 500000LL;
using namespace std;
typedef unsigned long long ull;
typedef  long long ll;


ll N;
vector<vector<pair<ll,ll>>> g1;
vector<ll> g2;
vector<ll> d;
ll dfs(ll x, ll pre, ll cur) {
	ll res = 0;
	d[x] = cur;
	for (pair<ll,ll> xx : g1[x]) {
		if (xx.first == pre) continue;
		res += dfs(xx.first, x, cur + 1) + 1;
	}

	return g2[x] = res;
}

int main()
{
	cin >> N;
	g1.resize(N);
	g2 = vector<ll>(N, 0);
	d.resize(N);
	vector<tuple<ll, ll, ll>> vt(N - 1);
	for (ll i = 0; i < N - 1; i++) {
		ll u, v, w;
		cin >> u >> v >> w;
		u--;
		v--;
		vt[i] = make_tuple(u, v, w);
		g1[u].push_back(make_pair(v, w));
		g1[v].push_back(make_pair(u, w));
	}

	dfs(0, -1, 0);

	ll res = 0;
	for (ll i = 0; i < N - 1; i++) {
		ll u, v, w;
		tie(u, v, w) = vt[i];
		if (d[u] > d[v]) {
			swap(u, v);
		}
		ll l = N - g2[v] - 1;
		ll r = g2[v] + 1;
		res += w * l * r * 2;
	}

	cout << res << endl;
	return 0;
}