fun main(args: Array<String>) {
    val stageCount = readLine()!!.toInt()
    (1..stageCount).forEach {
        stageList[it] = TreeNode(it)
    }
    (1..stageCount).forEach {
        val (l, s) = readLine()!!.split(" ").map { it.toInt() }
        stageList[it]!!.value = l * 10
        stageList[it]!!.parent = stageList[s]!!
        stageList[s]!!.items.add(stageList[it]!!)
    }
    var ans = 0
    (1..stageCount).forEach {
        var sublist = stageList.filter {  it.value.parent == null && !it.value.clearFlag }
        if(sublist.isEmpty()) {
            sublist = stageList.filter { !it.value.clearFlag }
        }
        val cur = sublist.minBy { it.value.value }!!.value
        ans += cur.value
        cur.clearFlag = true
        cur.parent?.let {
            it.items.remove(cur)
        }
        cur.parent = null
        cur.items.forEach{
            it.value = it.value / 2
            it.parent = null
        }
        cur.items.clear()
    }
    println(ans.toDouble()/10)
}

val stageList = mutableMapOf<Int, TreeNode>()

class TreeNode(val id:Int) {
    var parent:TreeNode? = null
    var clearFlag = false
    var items = mutableListOf<TreeNode>()
    var value = 0
}