fun main(args:Array<String>):Unit {
    val (n, m, d) = readLine()!!.trim().split(' ').map(String::toDouble)
    println(
            String.format("%.10f",
                    if (d != 0.0) 2.0 * (n - d) / n / n * (m - 1)
                    else 1.0 / n * (m - 1)
            )
    )
}