import java.util.*;
import java.io.*;

public class Main {
    static long[] chiledren;
    static long[] costs;
    static HashMap<Integer, Integer>[] graph;
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        graph = new HashMap[n];
        for (int i = 0; i < n; i++) {
            graph[i] = new HashMap<Integer, Integer>();
        }
        for (int i = 0; i < n - 1; i++) {
            String[] line = br.readLine().split(" ", 3);
            int a = Integer.parseInt(line[0]) - 1;
            int b = Integer.parseInt(line[1]) - 1;
            int c = Integer.parseInt(line[2]);
            graph[a].put(b, c);
            graph[b].put(a, c);
        }
        chiledren = new long[n];
        costs = new long[n];
        getChildrenCount(0, -1);
        long total = 0;
        for (int i = 0; i < n; i++) {
            total += chiledren[i] * (n - chiledren[i]) * costs[i];
        }
        System.out.println(total * 2);
    }
    
    static long getChildrenCount(int to, int from) {
        for (Map.Entry<Integer, Integer> entry : graph[to].entrySet()) {
            int x = entry.getKey();
            if (x == from) {
                costs[to] += entry.getValue();
            } else {
                chiledren[to] += getChildrenCount(x, to);
            }
        }
        chiledren[to]++;
        return chiledren[to];
    }
}