#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

using ll = long long;
using P = pair<int, int>;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n;
    cin >> n;
    vector<vector<P>> g(n);
    for(int i = 1; i < n; ++i){
        int u, v, w;
        cin >> u >> v >> w;
        --u, --v;
        g[u].emplace_back(v, w);
        g[v].emplace_back(u, w);
    }

    vector<int> subtree_size(n, 1);
    ll ans = 0;
    auto dfs = [&](auto&& self, int from = 0, int par = -1) -> int {
        for(auto [to, cost] : g[from]){
            if(to == par)   continue;
            subtree_size[from] += self(self, to, from);
            ans += (ll)cost * subtree_size[to] * (n - subtree_size[to]);
        }
        return subtree_size[from];
    };
    dfs(dfs);
    
    cout << ans * 2 << endl;

    return 0;
}