Add code in between paragraphs on single posts page

functions.php

//Insert ads after second and fifth paragraph of single post content. 
add_filter( 'the_content', 'prefix_insert_post_ads' );
function prefix_insert_post_ads( $content ) {
    // Add your ads code here
    $ad_code = '<div>Ads code goes here</div>';
    if ( is_single() && ! is_admin() ) {
    	/* Change the paragraph number as per your preference, currently with the following code the Ads code can be added after the second and fifth paragraph */
        return prefix_insert_after_paragraph( $ad_code, array( 2, 5 ) , $content );
    }
    return $content;
}

// Parent Function that makes the magic happen
function prefix_insert_after_paragraph( $insertion, $paragraph_id, $content ) {
    $closing_p = '</p>';
    $paragraphs = explode( $closing_p, $content );
    foreach ($paragraphs as $index => $paragraph) {
        if ( trim( $paragraph ) ) {
            $paragraphs[$index] .= $closing_p;
        }
        foreach ( $paragraph_id as $id ){ 
	         if ( $id == $index + 1 ) {
	            $paragraphs[$index] .= $insertion;
	        }
        }
    }
    return implode( '', $paragraphs );
}