#!/usr/bin/env python3
import sys

def main():
    sys.setrecursionlimit(10 ** 9)
    ans = 0
    N = int(input())
    costs = [[0] * N for _ in range(N)]
    class DFS():
        def __init__(self, N: int) -> None:
            self.nodes = N                          # 頂点数
            self.G = [[] for _ in range(N)]         # グラフ
            self.seen = [False] * N                 # 各ノードが訪問済みかどうかのフラグ
            self.firstOrder = []                    # ノードの行きがけ順(0-index)
            self.lastOrder = []                     # ノードの帰りがけ順(0-index)

        # 辺の追加
        def addEdge(self, fromNode: int, toNode: int, bothDirection: bool):
            self.G[fromNode].append(toNode)
            if bothDirection:
                self.G[toNode].append(fromNode)
        # DFS
        def build(self, now: int, pre:int):
            sum = 0
            nonlocal ans
            # ----- ノードに到着した時の処理
            self.firstOrder.append(now)
            self.seen[now] = True
            # ----- 隣接する各ノードへの移動処理
            for next in self.G[now]:
                if self.seen[next]:
                    continue
                sum += self.build(next, now)
            # ----- ノードから戻る時の処理
            # self.lastOrder.append(now)
            sum += 1
            ans += sum * (self.nodes - sum) * costs[pre][now]
            return sum
    
    d = DFS(N)
    for _ in range(N - 1):
        u, v, w = map(int, input().split())
        costs[u - 1][v - 1] = w
        costs[v - 1][u - 1] = w
        d.addEdge(u - 1, v - 1, bothDirection=True)
    d.build(0, -1)
    print(ans * 2)

if __name__ == '__main__':
    main()