How to get last number of page in category?

Question

I want to show last number of page in pagination only.

The code of pagination comes from below path.

/var/www/html/magento/vendor/magento/module-theme/view/frontend/templates/html/pager.phtml

I'm using below code to get last category page.

<?php 
$current_page =  $this->getRequest()->getParam("p");
$objectManager =  \Magento\Framework\App\ObjectManager::getInstance();
$categoryFactory = $objectManager->get('\Magento\Catalog\Model\CategoryFactory');
$categoryId = $this->getrequest()->getParam(3); // YOUR CATEGORY ID
$category = $categoryFactory->create()->load($categoryId);

$productCollectionFactory = $objectManager->get('\Magento\Catalog\Model\ResourceModel\Product\CollectionFactory');
            $collection = $productCollectionFactory->create();

            $collection->addAttributeToSelect('*');
            $collection->addCategoryFilter($category);
            $collection->setCurPage($current_page)->setPageSize(12);


echo $collection->getLastPageNumber();
 ?>

I could not get last page from this.