#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) begin(v),end(v)
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using pii = pair<int, int>;
constexpr ll INF = 1ll<<30;
constexpr ll longINF = 1ll<<60;
constexpr ll MOD = 1000000007;
constexpr bool debug = false;
//---------------------------------//

int main() {
	int N;
	cin >> N;
	vector<vector<pii>> g(N);
	REP(i, N - 1) {
		int u, v, w;
		scanf("%d %d %d", &u, &v, &w);
		--u; --v;
		g[u].emplace_back(v, w);
		g[v].emplace_back(u, w);
	}
	
	vector<int> child(N), par(N);
	auto dfs = [&](auto self, int u) -> int {
		child[u] = 1;
		for (auto [v, _] : g[u]) {
			if (v == par[u]) continue;
			par[v] = u;
			child[u] += self(self, v);
		}
		return child[u];
	};
	
	par[0] = -1;
	dfs(dfs, 0);
	
	ll ans = 0;
	REP(u, N) for (auto [v, w] : g[u]) {
		if (par[v] != u) continue;
		ans += (ll)child[v] * (N - child[v]) * w;
	}
	cout << ans * 2 << endl;
}