Excerpt for POSTS and RSS – two different length

I want to add two different excerpts for posts and RSS feed

Excerpt for posts need to be long 30 words but for RSS need to be 105 words.

Currently I use functions.php for excerpt with code:

<?php
function website_excerpt_length( $length ) {
	return 105;
}
add_filter( 'excerpt_length', 'website_excerpt_length' );
?>

and have the same length excerpt

How can I implement two excerpts for RSS and regular post?

Thank you WP people !