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

def dfs(f,p):
    for t,w in edge[f]:
        if t == p:
            continue
        dfs(t,f)
    if p != -1:
        size[p] += size[f]

dfs(0,-1)
ans = 0
for i in range(N):
    for j,w in edge[i]:
        M = min(size[i],size[j])
        ans += M*(N-M)*w
print(ans)