INF = 10 ** 7
import sys
input = sys.stdin.readline
sys.setrecursionlimit(100000000)
dy = (-1,0,1,0)
dx = (0,1,0,-1)

MAXN = 200005
G = [[] for _ in range(MAXN)]

ans = 0
def dfs(i,n,p = -1):
    global ans
    ret = 1
    for e,c in G[i]:
        if e == p:
            continue
        tmp = dfs(e,n,i)
        ans += 2 * tmp * (n - tmp) * c
        ret += tmp
    return ret

def main():
    n = int(input())
    for _ in range(n - 1):
        a,b,c = map(int,input().split())
        a -= 1
        b -= 1
        G[a].append((b,c))
        G[b].append((a,c))
    
    dfs(0,n)
    global ans
    print(ans)
if __name__ == '__main__':
    main()