fun main()
{
  val n = readLine()!!.toInt()
  val ct = Array<Long>(n+1){ 1L }
  for (i in 2..n) {
    var x = i
    while (x <= n) {
      ct[x]++
      x += i
    }
  }
  var ans = 0L
  for (i in 1..n) {
    ans += ct[i] * i
  }
  println(ans)
}