@Echo off
set k=0
:start
if %k% lss 20 goto echo
exit/b
:echo
set /a k=k+1
for /f %%i in ('find /v /c ""^<%k%.txt') do set num=%%i
set/a _num=%num%-10
for /f "skip=10 tokens=1* delims=:" %%i in ('findstr /n .* %k%.txt') do if %%i lss %_num% echo. %%j>>result%k%.txt
goto start