local k = io.read("*n")
k = k + 1
local t = {}
t[1] = 1
for i = 2, k do
  t[i] = 0
end
local rem = 1
local e = 0
local cnt = 0
while(0.00001 < rem) do
  cnt = cnt + 1
  -- GOAL
  local tmp = t[k - 1]
  if(2 < k) then tmp = tmp +  t[k - 2] end
  if(3 < k) then tmp = tmp +  t[k - 3] end
  if(4 < k) then tmp = tmp +  t[k - 4] end
  if(5 < k) then tmp = tmp +  t[k - 5] end
  if(6 < k) then tmp = tmp +  t[k - 6] end
  e = e + cnt * tmp / 6
  rem = rem - tmp / 6
  -- START
  local st = t[k - 1] * 5
  if(2 < k) then st = st + t[k - 2] * 4 end
  if(3 < k) then st = st + t[k - 3] * 3 end
  if(4 < k) then st = st + t[k - 4] * 2 end
  if(5 < k) then st = st + t[k - 5] end
  st = st / 6
  -- MID
  for i = k - 1, 2, -1 do
    t[i] = t[i - 1]
    if(2 < i) then t[i] = t[i] + t[i - 2] end
    if(3 < i) then t[i] = t[i] + t[i - 3] end
    if(4 < i) then t[i] = t[i] + t[i - 4] end
    if(5 < i) then t[i] = t[i] + t[i - 5] end
    if(6 < i) then t[i] = t[i] + t[i - 6] end
    t[i] = t[i] / 6
  end
  t[1] = st
end
print(string.format("%.8f", e))