import java.util.Scanner

import scala.math.BigDecimal.RoundingMode

object Main extends App {
  val sc = new Scanner(System.in)
  val (a, b, n) = (sc.nextInt(), sc.nextLong(), sc.nextLong())

  val bDecimal = BigDecimal(b)
  println(floor(a * n / bDecimal) - a * floor(n / bDecimal).toLong)
  
  def floor(bd: BigDecimal) = bd.setScale(0, RoundingMode.FLOOR)
}
