import java.util.Scanner

import scala.io.StdIn._
object Main extends App {

  val n = scala.io.StdIn.readInt()

  def solve(): Long = {
    (1 to n).foldLeft(0L) { (acc, num) =>
      acc + num * sumToN(n/num)
    }
  }

  def sumToN(n: Long): Long = n * (n + 1) / 2


  println(solve())

}

