import kotlin.math.max
import kotlin.math.min

// なんか本番でエラーでる
private val isDebug = runCatching {
  System.getenv("MY_DEBUG") != null
}.fold({it}, {false})

private fun readLn() = readLine()!!
private fun readInt() = readLn().toInt()
private fun readStrings() = readLn().split(" ")
private fun readInts() = readStrings().map { it.toInt() }.toIntArray()
private fun readLongs() = readStrings().map { it.toLong() }.toLongArray()
private fun debug(msg: () -> String) {
  if (isDebug) System.err.println(msg())
}
private fun debug(a: IntArray) {
  if (isDebug) debug{a.joinToString(" ")}
}

val MOD = 1000000007

data class Entry(val i: Int, val x: Long)

fun main() {
  val N = readInt()
  val g = Array<MutableList<Int>>(N){ mutableListOf()}
  val U = IntArray(N - 1)
  val V = IntArray(N - 1)
  val W = IntArray(N - 1)
  repeat(N - 1) {
    var (u, v, w) = readInts()
    u--; v--
    g[u].add(v)
    g[v].add(u)
    U[it] = u
    V[it] = v
    W[it] = w
  }
  val (p, q) = traceBfs(g)
  val dp = IntArray(N)
  for (i in N - 1 downTo 0) {
    val v = q[i]
    dp[v]++ // 自分
    for (u in g[v]) {
      if (u != p[v]) {
        dp[v] += dp[u]
      }
    }
  }
  debug(dp)
  debug(p)
  debug(q)

  var ans = 0L
  for (i in 0 until N - 1) {
    val cnt = if (p[U[i]] == V[i]) {
      dp[U[i]]
    } else {
      dp[V[i]]
    }
    ans += cnt.toLong() * (N - cnt) * W[i] * 2
  }

  println(ans)
}

/**
 * (parent, queue)
 */
fun traceBfs(g: Array<MutableList<Int>>, rt: Int = 0): Array<IntArray> {
  val n = g.size
  val q = IntArray(n)
  val p = IntArray(n){-2}
  var cur = 0
  var last = 1
  p[0] = -1
  q[0] = rt
  while (cur < last) {
    val v = q[cur++]
    for (u in g[v]) {
      if (p[u] == -2) {
        p[u] = v
        q[last++] = u
      }
    }
  }
  return arrayOf(p, q)
}