import java.util.*

fun main() {
    val builder = StringBuilder()

    val (n, m, c) = readInputLine().split(" ").map { it.toLong() }

    val aList = readInputLine().split(" ").map { it.toLong() }
    val bList = readInputLine().split(" ").map { it.toLong() }.sorted()

    var cnt = 0L

    for (a in aList) {
        cnt += m - upperBound(bList, c / a).toLong()
    }

    builder.appendln(cnt.toDouble() / (n * m).toDouble())

    print(builder.toString())
}

fun readInputLine(): String {
    return readLine()!!
}

fun <T: Comparable<T>> upperBound(list: List<T>, value: T): Int {
    return Collections.binarySearch(list, value, {x, y -> if (x > y) 1 else -1}).inv()
}