rust, 151 bytes

Result

AC

Duration

1270ms

Code [DL]

use std::io::*;fn main(){let mut a=[0;9999];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

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                   K                              

stdout

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                   k!!!!!!!!u

stderr

warning: unused `std::result::Result` that must be used
 --> /tmp/code.rs:1:45
  |
1 | use std::io::*;fn main(){let mut a=[0;9999];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:1:126
  |
1 | use std::io::*;fn main(){let mut a=[0;9999];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