elixir, 136 bytes

Result

AC

Duration

1852ms

Code [DL]

defmodule M do
def f(x)do
""<>c=IO.read(1)
IO.write(if x<1,do: "@",else: c)
f(case c do"T"->1
"K"->x-50
_->rem(x+1,51)end)end
end
M.f(1)

stdin

                            T                     
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                       K                          

stdout

                            T                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                            @                     
                       K@@@@@                     

stderr

** (MatchError) no match of right hand side value: :eof
    /volume/CODE:3: M.f/1
    (elixir) lib/code.ex:767: Code.require_file/2

strace