import sys
readline = sys.stdin.readline
sys.setrecursionlimit(10**7)

def dfs(s, p=-1):
    global ans
    cnt = 1
    for u, c in G[s]:
        if u == p:
            continue
        n = dfs(u, s)
        ans += n * (N - n) * c
        cnt += n
    return cnt
            
            

N = int(readline())
G = [[] for i in range(N)]
for i in range(N - 1):
    u, v, w = map(int, readline().split())
    u, v = u - 1, v - 1
    G[u].append([v, w])
    G[v].append([u, w])
    
ans = 0
dfs(0)
print(ans * 2)