I want to delete 1 frame every 12 frames of the video. The original video has a frame rate of 30, so after deleting it, it becomes 28. How should I write this operation using ffmpeg?

I used the following command, but there is a problem, the new video generated will be shorter than the original video

ffmpeg -y -r 28 -vsync 0 -i demo.mp4 -vf “select=’mod(n+4,12)’,setpts=’N/28/TB'” “demo_2.mp4”

Please help me how should I do it, thanks