import scala.io.{StdIn => in}

object Main extends App {
  val Array(a, b, c, d) = in.readLine.split(" ").map(_.toLong)

  val a1 = b / c
  val a2 = (a-1) / c
  val b1 = b / d
  val b2 = (a-1) / d

  val a3 = a1 - a2
  val b3 = b1 - b2

  def gcd(a:Long, b:Long):Long = {
    if(b == 0) a
    else gcd(b, a%b)
  }

  val lcm = c * d / gcd(c, d)

  val c1 = b / lcm
  val c2 = (a-1) / lcm

  val c3 = c1 - c2

  val ans = if(c == 1 || d == 1) 0 else ((b - (a-1)) - (a3 + b3 - c3)) max 0
  println(ans)
}