fun main(args: Array<String>) {
  val inputs = readLine()
  if (inputs == null) return
  val (n, m, d) = inputs.split(" ").map { it.toInt() }
  val averageBeautifulnessPerPair = (n - d).toDouble() * (if (d == 0) 1 else 2 ) / n / n
  val averageBeautifulness = averageBeautifulnessPerPair * (m - 1)
  println(String.format("%.7f", averageBeautifulness))
}
