import scala.io.StdIn

object Main extends App {

  val Array(a, b, n) = StdIn.readLine().split(" ").map(_.toLong)
  val x = if (b > 1) n / (b - 1) * (b - 1) else 0
  println(if (x > 0) f(x) else f(n))

  def f(x: Long) = (a * x) / b - a * (x / b)

  def readIntPair: (Int, Int) = {
    val Array(x, y) = StdIn.readLine().split(" ").map(_.toInt)
    (x, y)
  }

  def readIntArr = StdIn.readLine().split(" ").map(_.toInt)
}