elixir, 143 bytes

Result

WA

Duration

1894ms

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
:eof->1/0
"T"->1
"K"->x-50
_->rem(x+1,51)end)end
end
M.f(1)

stdin

                                     T            
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
          K                                       

stdout

                                     T            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
                                     @            
          K@@@@@@@@@@@@@@@@@@@@@@@@@@@            
eof

stderr

warning: this expression will fail with ArithmeticError
  /volume/CODE:6

** (ArithmeticError) bad argument in arithmetic expression
    /volume/CODE:6: M.f/1
    (elixir) lib/code.ex:767: Code.require_file/2

strace