"""

https://yukicoder.me/problems/no/872

"""

import sys
from sys import stdin

sys.setrecursionlimit(300000)

N = int(input())

lis = [ [] for i in range(N) ]

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


def dfs(v,p):
    cnum = 1
    ans = 0
    for nex,w in lis[v]:
        if nex != p:
            nans,nc = dfs(nex,v)
            ans += nans + w * nc * (N-nc)
            cnum += nc

    return ans,cnum

print (dfs(0,-1)[0] * 2)