k = gets.to_i
a = Array.new(k + 6, 1.0)
b = Array.new(k + 6, 0.0)
a[k] = 0
b[k] = 0
(k - 1).downto(0){|i|
    a[i] = a[(i + 1)..(i + 6)].inject(:+) / 6
    b[i] = b[(i + 1)..(i + 6)].inject(:+) / 6 + 1
    }
p b[0] / (1 - a[0])