n = gets.to_i
if n == 0 then
  p 4
  exit()
end
a = Array.new(101)
a[0] = 1
a[1] = 3
k = 1
2.upto(n) {|i|
  a[i] = a[i-1]*19 - a[i-2]*12*4
  k *= 4
}
s = a[n]
ans = (s/k).to_s + "."
s = s%k*10;
20.times{
  ans += (s/k).to_s
  s = s%k * 10;
}
puts ans