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<?php 

function get_primary_cat_id($id=Null){

	if(!$id){
		$id = get_the_ID();
	}

	if(get_post_type($id)!="post"){
		$meta_value = "_yoast_wpseo_primary_" .  get_post_type($id). "_cat";
	} else{
		$meta_value = "_yoast_wpseo_primary_category";
	}


	$primary_category_id = get_post_meta($id, $meta_value,true);

	if(!$primary_category_id){
		$primary_category_id = get_the_category($id);
	}

	$primary_category_id = (int)$primary_category_id;
	
	return $primary_category_id;

}