using System; using System.Collections.Generic; using System.Linq; using System.IO; using static System.Console; using static System.Convert; using static System.Math; //using static System.Globalization.CultureInfo; using System.Text; class Program { public static bool chmin(ref T num, T val) where T : IComparable { if (num.CompareTo(val) == 1) { num = val; return true; } return false; } public static bool chmax(ref T num, T val) where T : IComparable { if (num.CompareTo(val) == -1) { num = val; return true; } return false; } public static void swap(ref T v1, ref T v2) { var t = v2; v2 = v1; v1 = t; } static void Main(string[] args) { var pr = new Program(); var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false }; Console.SetOut(sw); pr.Solve(); Console.Out.Flush(); } int[] ct; List>[] edge; long res; void Solve() { var num = Input.num; edge = Input.edge>(num); for(var i = 0; i < num - 1; i++) { var uvw = Input.ar; uvw[0]--;uvw[1]--; edge[uvw[0]].Add(new Pair(uvw[2], uvw[1])); edge[uvw[1]].Add(new Pair(uvw[2], uvw[0])); } ct = new int[num]; dfs(0, -1); ddfs(0, -1); WriteLine(res); } int dfs(int index,int pa) { var c = 1; foreach (var e in edge[index]) if (e.v2 != pa) { c += dfs(e.v2, index); } return ct[index] = c; } void ddfs(int index, int pa) { foreach (var e in edge[index]) if (e.v2 != pa) { res += 2L * ct[e.v2] * (edge.Length - ct[e.v2]) * e.v1; ddfs(e.v2, index); } } } public class Input { public static string read => ReadLine().Trim(); public static int[] ar => read.Split(' ').Select(int.Parse).ToArray(); public static int num => ToInt32(read); public static long[] arL => read.Split(' ').Select(long.Parse).ToArray(); public static long numL => ToInt64(read); public static T[] create(int n, Func f) => Enumerable.Repeat(0, n).Select(f).ToArray(); public static char[][] grid(int h) => create(h, _ => read.ToCharArray()); public static int[] ar1D(int n) => create(n, _ => num); public static long[] arL1D(int n) => create(n, _ => numL); public static string[] strs(int n) => create(n, _ => read); public static int[][] ar2D(int n) => create(n, _ => ar); public static long[][] arL2D(int n) => create(n, _ => arL); public static List[] edge(int n) => create(n, _ => new List()); public static T GetValue(string g) { var t = typeof(T); if (t == typeof(int)) return (T)(object)int.Parse(g); if (t == typeof(long)) return (T)(object)long.Parse(g); if (t == typeof(string)) return (T)(object)g; if (t == typeof(char)) return (T)(object)char.Parse(g); if (t == typeof(double)) return (T)(object)double.Parse(g); if (t == typeof(bool)) return (T)(object)bool.Parse(g); return default(T); } public static void Make(out T1 v1, out T2 v2) { v1 = Next(); v2 = Next(); } public static void Make(out T1 v1, out T2 v2, out T3 v3) { Make(out v1, out v2); v3 = Next(); } public static void Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4) { Make(out v1, out v2, out v3); v4 = Next(); } public static void Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5) { Make(out v1, out v2, out v3, out v4); v5 = Next(); } public static void Make(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5, out T6 v6) { Make(out v1, out v2, out v3, out v4, out v5); v6 = Next(); } private static Queue sc; public static T Next() { sc = sc ?? new Queue(); if (sc.Count == 0) foreach (var item in read.Split(' ')) sc.Enqueue(item); return GetValue(sc.Dequeue()); } public static void Next(ref T val) => val = Next(); public const long Inf = (long)1e18; public const double eps = 1e-6; public const string Alfa = "abcdefghijklmnopqrstuvwxyz"; public const int MOD = 1000000007; } public class Pair : IComparable> { public T1 v1 { get; set; } public T2 v2 { get; set; } public Pair() { v1 = Input.Next(); v2 = Input.Next(); } public Pair(T1 v1, T2 v2) { this.v1 = v1; this.v2 = v2; } public int CompareTo(Pair p) { var c = Comparer.Default.Compare(v1, p.v1); if (c == 0) c = Comparer.Default.Compare(v2, p.v2); return c; } public override string ToString() => $"{v1.ToString()} {v2.ToString()}"; public override bool Equals(object obj) => this == (Pair)obj; public override int GetHashCode() => v1.GetHashCode() ^ v2.GetHashCode(); public static bool operator ==(Pair p1, Pair p2) => p1.CompareTo(p2) == 0; public static bool operator !=(Pair p1, Pair p2) => p1.CompareTo(p2) != 0; public static bool operator >(Pair p1, Pair p2) => p1.CompareTo(p2) == 1; public static bool operator >=(Pair p1, Pair p2) => p1.CompareTo(p2) != -1; public static bool operator <(Pair p1, Pair p2) => p1.CompareTo(p2) == -1; public static bool operator <=(Pair p1, Pair p2) => p1.CompareTo(p2) != 1; } public class Pair : Pair, IComparable> { public T3 v3 { get; set; } public Pair() : base() { v3 = Input.Next(); } public Pair(T1 v1, T2 v2, T3 v3) : base(v1, v2) { this.v3 = v3; } public int CompareTo(Pair p) { var c = base.CompareTo(p); if (c == 0) c = Comparer.Default.Compare(v3, p.v3); return c; } public override string ToString() => $"{base.ToString()} {v3.ToString()}"; }