# nadare様のコード参考
# https://yukicoder.me/submissions/374115

N = int(input())
T = [[] for i in range(N)]
E = []
for i in range(N - 1):
    a, b, w = map(int, input().split())
    a, b = a - 1, b - 1
    T[a].append(b)
    T[b].append(a)
    E.append([a, b, w])


class TwoDividedTree:
    def __init__(self, n, tree):
        self.tree = tree
        self.depth = [-1] * n
        self.size = [1] * n

        self.calc()

    def calc(self):
        self.depth[0] = 0
        stack = [0]
        rev_directions = []  # 深いところから根に辿る辺の集合

        while stack:
            fr = stack.pop()
            for to in self.tree[fr]:
                if self.depth[to] != -1:
                    continue

                self.depth[to] = self.depth[fr] + 1
                stack.append(to)
                rev_directions.append([fr, to])

        while rev_directions:
            parent, child = rev_directions.pop()
            self.size[parent] += self.size[child]

    '''
    辺（a, b） で木を２分割した時の、片方のサイズ
    '''
    def size_after_divided(self, a, b):
        if self.depth[a] < self.depth[b]:
            a, b = b, a
        return self.size[a]


tdt = TwoDividedTree(N, T)
ans = 0
for a, b, w in E:
    s = tdt.size_after_divided(a, b)
    ans += 2 * s * (N - s) * w

print(ans)