Apply code to only first post

first-post.php

<?php if (have_posts()) : ?>
<?php $post = $posts[0]; $c=0;?>
<?php while (have_posts()) : the_post(); ?>

<?php $c++;
if( $c == 1) :?>
<h1>The first post on the main index page</h1>
<?php the_title(); ?>
<?php the_excerpt(); ?>

<?php else :?>
<h2><?php the_title(); ?></h2>
<?php the_content(); ?>
<?php endif;?>

<?php endwhile; ?>

<!-- page nav -->
<?php endif; ?>`