rust, 178 bytes

Result

AC

Duration

1242ms

Code [DL]

use std::io::*;fn main(){let mut a:[u8;999]=[0;999];let m=stdin().read(&mut a).unwrap();let mut i=51;while a[i-1]!=117{a[i]=a[i]|a[i-51]|a[i-1]&1;i+=1;}stdout().write(&a[0..m]);}

stdin

             T                                    
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
   K                                              

stdout

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   k!!!!!!!!!u                                    

stderr

warning: unused `std::result::Result` that must be used
 --> /tmp/code.rs:1:153
  |
1 | use std::io::*;fn main(){let mut a:[u8;999]=[0;999];let m=stdin().read(&mut a).unwrap();let mut i=51;while a[i-1]!=117{a[i]=a[i]|a[i-51]|a[i-1]&1;i+=1;}stdout().write(&a[0..m]);}
  |                                                                                                                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(unused_must_use)] on by default
  = note: this `Result` may be an `Err` variant, which should be handled

strace