//include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <unordered_map>
#include <climits>
#include <set>
#include <unordered_set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <queue>
#include <random>
#include <complex>
#include <regex>
#include <locale>
#include <random>
#include <type_traits>

using namespace std;

#define SHOW_VECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOW_MAP(v){std::cerr << #v << endl; for(const auto& xxx: v){std::cerr << xxx.first << " " << xxx.second << "\n";}}

using LL = long long;

//------------------------------------------
//------------------------------------------

constexpr int MAX = 200020;

struct edge {
    int to;
    LL cost;
};

vector<edge> G[MAX];

LL dfs(int v, int p, LL N, LL &ans) {
    LL ret = 0;
    for (auto e: G[v]) {
        int to = e.to;
        LL cost = e.cost;
        if (to == p) continue;
        LL a = dfs(to, v, N, ans);
        ans += cost * a * (N - a);
        ret += a;
    }
    return ret + 1;
}

int main() {

    int N;
    cin >> N;

    for (int i = 0; i < N - 1; i++) {
        int a, b, c;
        cin >> a >> b >> c;
        a--, b--;
        G[a].push_back({b, c});
        G[b].push_back({a, c});
    }

    LL ans = 0;
    dfs(0, -1, N, ans);


    cout << ans * 2<< endl;

}