erlang, 146 bytes

Result

AC

Duration

1590ms

Code [DL]

#!
main(_)->f(0).
f(X)->C=io:get_chars("",1),Y=case C of"T"->0;"K"->X-50;eof->halt();_->X+1 end rem 51,io:put_chars(if Y<1->"@";true->C end),f(Y).

stdin

                                   T              
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
       K                                          

stdout

                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
                                   @              
       @@@@@@@@@@@@@@@@@@@@@@@@@@@@@              

stderr

strace