elixir, 216 bytes

Result

AC

Duration

2196ms

Code [DL]

defmodule F do
def f(s,t)do
case IO.gets("")do
:eof->IO.write String.slice(String.trim_trailing(t)<>String.duplicate("*",99),0,String.length String.trim_trailing s)
t->IO.write s
f s,t
end
end
end
F.f IO.gets(""),""

stdin

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      K                                           

stdout

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      K*****

stderr

strace