#include <bits/stdc++.h>

int ri() {
	int n;
	assert(scanf("%d", &n) == 1);
	return n;
}
int n;
std::vector<std::vector<std::pair<int, int> > > hen;
std::vector<int> size;
std::vector<int> parent;

int dfs(int i, int par) {
	parent[i] = par;
	int cur = 1;
	for (auto &j : hen[i]) {
		if (j.first == par) continue;
		cur += dfs(j.first, i);
	}
	return size[i] = cur;
}

int main () {
	n = ri();
	hen.resize(n);
	for (int i = 0; i + 1 < n; i++) {
		int a = ri() - 1;
		int b = ri() - 1;
		int c = ri();
		hen[a].push_back({b, c});
		hen[b].push_back({a, c});
	}
	size.resize(n);
	parent.resize(n);
	dfs(0, -1);
	int64_t res = 0;
	for (int i = 0; i < n; i++) {
		for (auto &j : hen[i]) {
			if (parent[j.first] == i) {
				res += j.second * (int64_t) size[j.first] * (n - size[j.first]);
			}
		}
	}
	std::cout << res * 2 << std::endl;
	
	
	return 0;
}