// #pragma GCC optimize ("Ofast")
// #pragma GCC optimize ("unroll-loops")
// #pragma GCC target ("avx,avx2,fma")
#include <bits/stdc++.h>

using std::cin, std::cout, std::cerr;
using ll = long long;

int main() {
    std::ios::sync_with_stdio(false);
    int n; cin >> n;
    std::vector<std::vector<std::pair<int, int>>> e(n + 1);
    for(int i = 1; i < n; i ++) {
        int u, v, w;
        cin >> u >> v >> w;
        e[u].push_back({v, w});
        e[v].push_back({u, w});
    }

    ll ans = 0;
    std::vector<int> sz(n + 1);
    std::function<void(int, int)> dfs = [&](int x, int p) {
        sz[x] = 1;
        for(auto [i, w] : e[x]) if(i != p) {
            dfs(i, x);
            sz[x] += sz[i];
            ans += ll(w) * sz[i] * (n - sz[i]) * 2;
        }
    };
    dfs(1, 0);
    cout << ans << '\n';
}