local mmi, mma = math.min, math.max
local n = io.read("*n", "*l")
local s = io.read()
local t = {}
for i = 1, n do
  if s:sub(i, i) == "#" then
    table.insert(t, i)
  end
end
local ret = -1
local block = 1
for i = #t, 1, -1 do
  ret = mma(n + 1 - t[i], ret + 2)
  -- print(ret)
end
print(ret)