local n = io.read("*n")
local t = {}
t[1] = 1
for i = 2, n do
  local c = 0
  for j = 0, i - 1 do
    local a, b = j, i - j - 1
    if 0 < a then c = c + t[a] end
    if 0 < b then c = c + t[b] end
  end
  t[i] = 1 + c / i
end
print(string.format("%.10f", t[n]))