import strutils, sequtils, math

proc divisors(x: int) : seq[int] =
  result = newSeqWith(0, 0)
  var d = 1
  while d*d <= x:
    if x mod d == 0:
      result.add(d)
      var y = x div d
      if y != d:
        result.add(y)
    d += 1

var n = stdin.readLine.parseInt
var x = if (n and 1) == 1: n else: n shr 1
echo divisors(x).sum