rust, 160 bytes

Result

AC

Duration

1467ms

Code [DL]

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

stdin

                             T                    
                                                  
                                                  
                                                  
                                                  
                                                  
     K                                            

stdout

                             T                    
                             t                    
                             t                    
                             t                    
                             t                    
                             t                    
     k!!!!!!!!!!!!!!!!!!!!!!!u

stderr

warning: unused `std::result::Result` that must be used
 --> /tmp/code.rs:1:53
  |
1 | use std::io::*;fn main(){let mut a:[u8;999]=[0;999];stdin().read(&mut a);let mut i=51;while a[i-1]!=117{a[i]|=a[i-51]|a[i-1]&1;i+=1;}stdout().write(&a[0..i]);}
  |                                                     ^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(unused_must_use)] on by default
  = note: this `Result` may be an `Err` variant, which should be handled

warning: unused `std::result::Result` that must be used
 --> /tmp/code.rs:1:134
  |
1 | use std::io::*;fn main(){let mut a:[u8;999]=[0;999];stdin().read(&mut a);let mut i=51;while a[i-1]!=117{a[i]|=a[i-51]|a[i-1]&1;i+=1;}stdout().write(&a[0..i]);}
  |                                                                                                                                      ^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: this `Result` may be an `Err` variant, which should be handled

strace