object Sails2 extends Application {
  val N = readInt
  // 高さ,　旗の数
  val mast:Array[Array[int]] = List.tabulate(N, i => readLine.split(" ").toList.map(Integer.parseInt(_)).toArray).toArray
  var maxHeight = 0
  mast.foreach(l => maxHeight = Math.max(maxHeight, l(0)))

  val count = new Array[int](maxHeight + 1)
  var flags = 0
  mast.foreach(a => {
    count(a(0)) += 1
    flags += a(1)
  })
  for(i <- (1 to maxHeight - 1).reverse) {
    count(i) += count(i + 1)
  }
  var left = flags
  var sum = 0l
  for(i <- (1 to maxHeight).reverse) {
    val min = Math.min(count(i), left / i)
    left -= min
    sum += (min * (min - 1) / 2)
  }
  println(sum)
}