#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); i ++)
using namespace std;
typedef long long ll;
typedef pair<ll,ll> PL;
typedef pair<int,int> P;
const int INF = 1e9;
const ll MOD = 1e9 + 7;
const vector<int> dy = {-1,0,1,0};
const vector<int> dx = {0,1,0,-1};

const int MAXN = 200005;
vector<vector<PL>> G(MAXN);

ll ans = 0;
ll dfs(ll i,ll n,ll p = -1) {
    ll ret = 1;
    for (PL pa:G[i]) {
        ll e = pa.first;
        ll c = pa.second;
        if (e == p) continue;
        ll tmp = dfs(e,n,i);
        ans += 2 * tmp * (n - tmp) * c;
        ret += tmp;
    }
    return ret;
}

int main() {
    ll n; cin >> n;
    rep(_,n - 1) {
        int a,b,c; cin >> a >> b >> c;
        a --; b--;
        G[a].push_back(PL(b,c));
        G[b].push_back(PL(a,c));
    }
    dfs(0,n);
    cout << ans <<  endl;
    return 0;
}