#include<bits/stdc++.h>

#define int long long
using namespace std;
#define rep(i, n) for(int i=0;i<(n);++i)
typedef pair<int, int> pii;
const int INF = 1l << 60;
#define u_b upper_bound
#define l_b lower_bound

int N;
vector<pii> G[200200];
int Ans;

int dfs(int v, int p) {
    int children = 0;
    for (pii edge:G[v]) {
        if (edge.first == p)continue;
        int ch = dfs(edge.first, v) + 1;
        Ans += edge.second * (N - ch) * ch;
        children += ch;
    }
    return children;
}

signed main() {
    cin >> N;
    rep(i, N - 1) {
        int u, v, w;
        cin >> u >> v >> w;
        --u, --v;
        G[u].emplace_back(v, w);
        G[v].emplace_back(u, w);
    }
    dfs(0, -1);
    cout << 2 * Ans << endl;
    return 0;
}