from collections import deque

n=int(input())
v=[[] for i in range(n)]
for i in range(n-1):
    a,b,c=map(int,input().split())
    a-=1;b-=1
    v[a].append((b,c));v[b].append((a,c))
f=deque([(0,0,0)])
dp=[(0,0)]*n;ans=0
while f:
    q,w,e=f.pop()
    if len(v[q])>e:
        f.append((q,w,e+1))
        if w!=v[q][e][0]:
            f.append((v[q][e][0],q,0))
    else:
        a,b=0,1
        for i,j in v[q]:
            if i==w:
                continue
            ans+=a*dp[i][1]+dp[i][0]*b+j*dp[i][1]*b
            a+=dp[i][0]+j*dp[i][1]
            b+=dp[i][1]
        dp[q]=(a,b)
print(ans*2)