import java.io.{BufferedOutputStream, BufferedReader, InputStreamReader, PrintWriter}

object Main {
  def main(args: Array[String]): Unit = {
    val in = new BufferedReader(new InputStreamReader(System.in))
    val out = new PrintWriter(new BufferedOutputStream(System.out))
    val (a, b, n) = in.readLine().split("\\s+") match {
      case Array(a, b, n) => (a.toLong, b.toLong, n.toLong)
    }

    if (n + 1 >= b) {
      val k = (n + 1) / b
      out.println(a * k - Math.ceil(1.0 * a / b).toLong - a * (k - 1))
    } else {
      out.println(a * n / b)
    }
    out.flush()
  }
}
