import java.util.Scanner

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

  val bDouble = b.toDouble
  println(f(Math.min(b -1, n)))

  def f(x: Long): Int = (Math.floor(a * x / bDouble) - a * Math.floor(x / bDouble)).toInt
}
