using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var map = NArr(n - 1);
        var tree = new List<(int to, int len)>[n];
        for (var i = 0; i < tree.Length; ++i) tree[i] = new List<(int to, int len)>();
        foreach (var edge in map)
        {
            tree[edge[0] - 1].Add((edge[1] - 1, edge[2]));
            tree[edge[1] - 1].Add((edge[0] - 1, edge[2]));
        }
        var count = new int[n];
        WriteLine(DFS(n, 0, -1, tree, count));
    }
    static long DFS(int n, int cur, int prev, List<(int to, int len)>[] tree, int[] count)
    {
        var ans = 0L;
        ++count[cur];
        foreach (var next in tree[cur])
        {
            if (next.to == prev) continue;
            ans += DFS(n, next.to, cur, tree, count);
            ans += (long)next.len * count[next.to] * (n - count[next.to]) * 2;
            count[cur] += count[next.to];
        }
        return ans;
    }
}