#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
using ll = long long ;
using P = pair<ll,ll> ;
const int INF = 1e9;
const int MOD = 1000000007;

int n = 200005;
vector<vector<P>> tree(n,vector<P>());
ll ans = 0;

ll dfs(int i,int before=-1){
    ll cnt = 0;
    for(P p:tree[i]){
        if(p.second == before) continue;
        ll c = dfs(p.second,i);
        ans += c * (n - c) * p.first;
        cnt += c;
    }
    return cnt + 1;
}


int main(){
    cin >> n;
    rep(i,n-1){
        int u,v;
        ll w;
        cin >> u >> v >> w;
        --u;--v;
        tree[u].push_back(P(w,v));
        tree[v].push_back(P(w,u));
    }

    dfs(0);
    ans *= 2;
    cout << ans << endl;
    return 0;
}