k = gets.to_i

a = Array.new(k, 0)
a[0] = 1

ans_prev = 0
ans = 0

t = 0 #サイコロを振った回数
loop do
  t += 1
  a_next = Array.new(k, 0)

  a.each_with_index do |n, i|
    next if n == 0
    for j in i+1..i+6 do
      if j < k then
        a_next[j] += n / 6.0
      elsif j > k then
        a_next[0] += n / 6.0
      else
        ans += t * n / 6.0
      end
    end
  end

  break if ans > 0 && ans == ans_prev

  a = a_next
  ans_prev = ans
end

puts ans