class Tree():
    def __init__(self, n, decrement=1):
        self.n = n
        self.edges = [[] for _ in range(n)]
        self._edge_label = [[] for _ in range(n)]
        self.root = None
        self.size = [1]*n       # number of nodes in subtree
        self.decrement = decrement

    def add_edge(self, u, v, i):
        u, v = u-self.decrement, v-self.decrement
        self.edges[u].append(v)
        self.edges[v].append(u)
        self._edge_label[u].append((v,i))
        self._edge_label[v].append((u,i))

    def add_edges(self, edges):
        for i, p in enumerate(edges):
            u, v = p
            u, v = u-self.decrement, v-self.decrement
            self.edges[u].append(v)
            self.edges[v].append(u)
            self._edge_label[u].append((v, i))
            self._edge_label[v].append((u, i))

    def set_root(self, root):
        root -= self.decrement
        self.depth = [-1]*self.n
        self.root = root
        self.par = [-1]*self.n
        self.depth[root] = 0
        self.edge_label = [-1]*self.n # labeled by child
        self.order = [root]
        next_set = [root]
        while next_set:
            p = next_set.pop()
            for q, i in self._edge_label[p]:
                if self.depth[q] != -1: continue
                self.par[q] = p
                self.depth[q] = self.depth[p]+1
                self.edge_label[q]=i
                self.order.append(q)
                next_set.append(q)
        for p in self.order[::-1]:
            for q in self.edges[p]:
                if self.par[p] == q: continue
                self.size[p] += self.size[q]


#########################################################################################################
import sys
input = sys.stdin.readline

N= int(input())
T = Tree(N,decrement=1)
W=[]
for i in range(N-1):
    x, y, w = map(int, input().split())
    T.add_edge(x,y,i)
    W.append(w)

T.set_root(1)
S=T.size[0]

res=0
for i in range(1,N):
    s=T.size[i]
    res+=s*(S-s)*W[T.edge_label[i]]

print(res*2)