different thumbnail for last post

diff-thumbnails-for-last-post.php

<?php while (have_posts()) : the_post(); ?>
<?php if (is_paged()) : ?>
<?php $postclass = ('regular'); ?>
<?php else : ?>
<?php $postclass = ($post == $posts[0]) ? 'featured' : 'regular'; ?>
<?php endif; ?>
<div class="<?php echo $postclass; ?>">
<div class="thumbnail">
	<!-- post thumbnail -->
		<?php if ( has_post_thumbnail()) : // Check if thumbnail exists ?>
			<a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>">
			<?php 
			// Use wp_query to check the current post we're on, and then check the post count.
			if ( isset( $wp_query ) && $wp_query->current_post == $wp_query->post_count ){
				the_post_thumbnail( array( 1920, 1080 ) ); // Large image
			} else {
				the_post_thumbnail( array( 583, 420 ) );
			}
			?>
			</a>
		<?php endif; ?>
		<!-- /post thumbnail -->
</div>
<detail>
		<!-- post title -->
		<h2>
			<a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a>
		</h2>
		<!-- /post title -->
<!-- post details -->
		<span class="date"><?php the_time('F j, Y'); ?> <?php the_time('g:i a'); ?></span>
		<span class="author"><?php _e( 'Published by', 'html5blank' ); ?> <?php the_author_posts_link(); ?></span>
		<span class="comments"><?php if (comments_open( get_the_ID() ) ) comments_popup_link( __( 'Leave your thoughts', 'html5blank' ), __( '1 Comment', 'html5blank' ), __( '% Comments', 'html5blank' )); ?></span>
		<!-- /post details -->
		<?php html5wp_excerpt('html5wp_index'); // Build your custom callback length in functions.php ?>
		<?php edit_post_link(); ?>
</detail>
	</div>
<?php comments_template() ?>
<?php endwhile ?>