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

long long N, ans = 0; 
vector<vector<pair<int,long long>>> edge;
vector<long long> scale;

void dfs(int curr, int prev, long long d){
	for(auto& e: edge[curr]){
		int next = e.first;
		if(next!=prev) dfs(next,curr,e.second);
	}
	if(prev == -1) return;
	scale[prev] += scale[curr];
	ans += d*scale[curr]*(N-scale[curr])*2;
}

int main() {
	cin >> N;
	edge.resize(N);
	scale.resize(N,1);
	for(int i = 0; i < N-1; ++i){
		int u,v,w;
		cin >> u >> v >> w;
		u--,v--;
		edge[u].push_back({v,w});
		edge[v].push_back({u,w});
	}
	dfs(0,-1,-1);
	cout << ans << endl;
    return 0;
}