n = gets.to_i
a = gets.split(" ").map &:to_i
b = gets.split(" ").map &:to_i
count = 0
win = 0
a.permutation(n).each do |_a|
  b.permutation(n).each do |_b|
    count += 1
    win += 1 if [*0...n].inject(0){|s, i| s += (_a[i] <=> _b[i])} > 0
  end
end
p 1.0 * win / count