a = 4r
b = 3r
n = gets.to_i
if(n > 0)
  (n-1).times do
    c = (19 * b - 12 * a) / 4
    a = b
    b = c
  end
else
  b = a
end
if(b >= 1)
  puts b.to_f
  exit
else
  s = "0."
  n = b.numerator
  d = b.denominator
  while(n > 0)do
    n *= 10
    s << ((n/d).to_s)
    n %= d
  end
  puts s
end