import scala.io.StdIn.readLine
import scala.io.StdIn.readInt
import java.util.Scanner
import java.util.ArrayList

object Main extends App {
  val sc = new Scanner(System.in)
  val A = sc.nextLong()
  val B = sc.nextLong()
  val N = sc.nextLong()
  val x = List(B-1, N).min
  println((A*x/B)-A*(x/B))

}