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)
    }

    var max = Long.MinValue
    var x = if (b - 1 < n) {
      b - 1
    } else {
      n
    }

    while (x <= n) {
      max = Math.max(max, a * x / b - a * (x / b))
      x += b
    }

    out.println(max)
    out.flush()
  }
}
