import sys
input = sys.stdin.readline

N=int(input())
EDGE=[[] for i in range(N+1)]

for j in range(N-1):
    u,v,w=map(int,input().split())
    EDGE[u].append((v,w))
    EDGE[v].append((u,w))


from collections import deque
Q=deque([1])
USE=[0]*(N+1)
USE[1]=1

SORT=[1]

while Q:
    x=Q.pop()

    for to,_ in EDGE[x]:
        if USE[to]==0:
            SORT.append(to)
            Q.append(to)
            USE[to]=1

SORT.reverse()
ANS=0
SCORE=[1]*(N+1)
USE=[0]*(N+1)

for s in SORT:
    USE[s]=1

    for to,w in EDGE[s]:
        if USE[to]==0:
            ANS+=(SCORE[s])*(N-SCORE[s])*w
            SCORE[to]+=SCORE[s]

print(ANS*2)