arequire 'matrix'

K = gets.to_i
ans = Matrix[*(0...K).map {|i|
               (0...K).map {|j|
               if j == 0
                 if i == 0
                   [K, 6].min
                 else
                   [(K - i) - 6, 0].min
                 end
               elsif j < i
                 0
               elsif j == i
                 6
               elsif j <= i + 6
                 -1
               else
                 0
               end
}}].lup.solve([6]*K)[0].to_f
puts ans