import java.io._
import java.util.StringTokenizer
import scala.util.control.Breaks.{breakable,break}

object Main extends App {
  val in = new InputReader(System.in)
  val pw = new PrintWriter(System.out)

  val N = in.next().toInt
  val p = new Array[Double](N+1)
  for (i <- 1 to N)
    p(i) = in.next().toDouble


  //
  val dp = Array.ofDim[Double](N+1, N+1)

  dp(0)(0) = 1.0
  for (i <- 1 to N)
    for (k <- 0 to N)
      if(k != 0)
        dp(i)(k) = dp(i-1)(k-1) * p(i) + dp(i-1)(k) * (1.0 - p(i))
      else
        dp(i)(k) = dp(i-1)(k) * (1.0 - p(i))

  println(dp(N).slice(N/2+1, N+1).sum)
}


class InputReader(stream: InputStream) {
  private val reader = new BufferedReader(new InputStreamReader(stream))
  private var tokenizer: StringTokenizer = new StringTokenizer(reader.readLine())
  def next(): String = {
    while (!tokenizer.hasMoreTokens()) {
      tokenizer = new StringTokenizer(reader.readLine())
    }
    tokenizer.nextToken()
  }
}

