#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define LLINF 9223372036854775807
#define MOD ll(1e9+7)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cerr<<#x<<": "<<x<<endl

vector<vector<pll>> graph;
vector<int> visited(200005,-1);
ll ans = 0;

ll dfs(ll now, ll n, ll w){
    visited[now] = 1;
    ll ret = 1;
    for(int i = 0; i < graph[now].size(); i++){
        if(visited[graph[now][i].first] == -1){
            ret += dfs(graph[now][i].first, n, graph[now][i].second);
        }
    }
    ans += 2*ret*(n-ret)*w;
    return ret;
}

int main(){
    ll n;
    cin >> n;

    graph.resize(n);
    for(int i = 0; i < n-1; i++){
        ll a, b, c;
        cin >> a >> b >> c;
        a--; b--;
        graph[a].push_back({b,c});
        graph[b].push_back({a,c});
    }

    dfs(0,n,0);
    cout << ans << endl;
    return 0;
}