import sys
sys.setrecursionlimit(10**6)
n = int(input())
adj = [[] for _ in range(n)]
for _ in range(n-1):
	u, v, w = map(int, input().split())
	adj[u-1].append([v-1, w])
	adj[v-1].append([u-1, w])

ans = 0
def dfs(x, parent):
	global ans
	child_num = 1
	for c, w in adj[x]:
		if c == parent:
			continue
		d = dfs(c, x)
		ans += 2*d*(n-d)*w
		child_num += d
	return child_num

dfs(0, -1)
print(ans)