#include<bits/stdc++.h>

using namespace std;

struct edge{
    int to;
    int cost;
};

vector<edge> G[200000];

long dfs(int v,int p, int n, long &ans){
    long ret = 0;
    for(edge e:G[v]){
        int to = e.to;
        int cost = e.cost;
        if(to == p)continue;
        long a = dfs(to,v,n,ans);
        ans += cost*a*(n-a);
        ret += a;
    }
    return ret + 1;
}

int main(){
    int n = 0;
    cin >> n;
    for(int i = 0; i < n-1; i++){
        int a , b , c ;
        cin >> a >> b >> c;
        G[a].push_back({b , c});
        G[b].push_back({a , c});
    }
    long ans = 0;
    
    dfs(1,-1,n,ans);
    
    cout << ans * 2 << endl;
}