calc, 96 bytes

Result

WA

Duration

1818ms

Code [DL]

=REPT(LEFT(A1;51);B2/51)&REPT(C3;C2)&REPT(B3;FIND(A3;A1)-C2),=LEN(A1)-50,=FIND(B3;A1)-B2-1
T,K, 

stdin

                                     T            
                                                  
                                                  
                          K                       

stdout

                                     T            
                                     T            
                                     T            
                         KKKKKKKKKKKKK

stderr

javaldx: Could not find a Java Runtime Environment!
Warning: failed to read path from javaldx
convert /tmp/code.csv -> /tmp/out/code.csv using filter : Text - txt - csv (StarCalc)

strace