n=gets.to_i
p=gets.split.map(&:to_f)

p p.inject([1]){|dp,pi|
  rpi = 1-pi
  dp.each_with_object([0]*(dp.size+1)).with_index{|(ai,newdp),j|
    newdp[j] += ai * rpi
    newdp[j+1] += ai * pi
  }
}[-n/2..-1].inject(:+)