#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#define popcount __builtin_popcount
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;
int n;
vector<P> g[200020];
ll w[200020];
int cnt[200020];
bool used[200020];
ll ans;
void dfs(int x){
	used[x]=1;
	cnt[x]=1;
	for(auto p:g[x]){
		int y=p.first;
		if(used[y]) continue;
		dfs(y);
		cnt[x]+=cnt[y];
		ans+=2*(ll)(n-cnt[y])*(ll)cnt[y]*w[p.second];
	}
}
int main()
{
	cin>>n;
	for(int i=0; i<n-1; i++){
		int u, v; cin>>u>>v>>w[i];
		u--; v--;
		g[u].push_back({v, i});
		g[v].push_back({u, i});
	}
	dfs(0);
	cout<<ans<<endl;
	return 0;
}