How to create a rule in htaccess?

Question

htaccess

Hello everyone, perhaps the question is tritely simple, but I did not find the answer to it, maybe I was looking badly ....
In general, there is a link
https://site.com/1530778610/2018/Jul/05/lake-u_8610.jpg
and there is a code

RewriteRule ^([0-9]+)/([0-9]+)/([0-9a-zA-Z_-]+)/([0-9]+)/(thumbnail+)/([0-9a-zA-Z\-\_]+)(\.jpg)$ /upload/$2/$3/$4/$1_sm.jpg  [NC,L]

for some reason, if lake-u_8610.jpg is present in the file name, then the file is not found, but if you remove it, then everything is fine, that is,
https://site.com/1530778610/2018/Jul/05/lakeu_8610.jpg
here and so the norms open, only - you put it, immediately the music found.
thanks for the help