#include <bits/stdc++.h>
#define rep(i, a, n) for(int i = a; i < n; i++)
#define int long long
using namespace std;
typedef pair<int, int> P;
const int mod = 1000000007;
const int INF = 1e18;

int n;
vector<P> G[200010];
int sz[200010];
int ans = 0;

int dfs(int v, int p){
    int cnt = 1;
    for(auto i : G[v]){
        if(i.first == p) continue;
        cnt += dfs(i.first, v);
    }
    sz[v] = cnt;
    return cnt;
}

void dfs2(int v, int p){
    for(auto i : G[v]){
        if(i.first == p) continue;
        ans += i.second * sz[i.first] * (n - sz[i.first]);
        dfs2(i.first, v);
    }
}

signed main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cin >> n;
    rep(i, 0, n - 1){
        int u, v, w;
        cin >> u >> v >> w;
        u--; v--;
        G[u].push_back({v, w});
        G[v].push_back({u, w});
    }
    dfs(0, -1);
    dfs2(0, -1);
    cout << ans * 2 << endl;
}