local n, k = io.read("*n", "*n")
if(2 <= k) then
  local cnt = 1
  for i = k + 1, n do
    cnt = cnt * 2
  end
  print(cnt)
else
  local cnt = 0
  for i = 2, n - 1 do
    local t = 1
    for j = i + 1, n do
      t = t * 2
    end
    t = t - 1
    cnt = cnt + t
  end
  print(cnt)
end