Genesis: Ad after third post's content

functions.php

add_action( 'genesis_after_post_content', 'we_category_ad' );
/**
 * Ad after third post's content
 *
 */
function we_category_ad() {
	global $wp_query;
	if( 2 == $wp_query->current_post ) 
		echo '<div class="ad">Ad Goes Here</div>';
}