N = gets.to_i

P = {}
P[0] = 1
(1..N).each{|n| P[n] = P[n-1] * n}

cost = 1
for n in 2..N do
  c1 = cost * n

  c2 = P[n-1] * 2

  sum = 0
  cnt = 0
  for x in 1..n-2 do
    for y in x+1..n-1 do
      sum += x * y
      cnt += 1
    end
  end
  c3 = cnt > 0 ? sum * (P[n] - P[n-1] * 2) / cnt : 0

  cost = c1 + c2 + c3
end

puts cost / P[N].to_f