You can use:
Options +FollowSymLinks
RewriteEngine On
RewriteBase /calendar/
RewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteRule ^ http://www.%{HTTP_HOST}%{REQUEST_URI} [R=301,NE,L]
RewriteRule ^([0-9]+)/?$ load.php?year=$1 [L,QSA]
RewriteRule ^([0-9]+)/(page)/([0-9]+)/?$ load.php?year=$1&p=$3 [L,QSA]
RewriteRule ^([0-9]+)/([0-9]+)/?$ load.php?year=$1&month=$2 [L,QSA]
RewriteRule ^([0-9]+)/([0-9]+)/(page)/([0-9]+)/?$ load.php?year=$1&month=$2&p=$4 [L,QSA]
RewriteRule ^([0-9]+)/([0-9]+)/([0-9]+)/?$ load.php?year=$1&month=$2&date=$3 [L,QSA]
RewriteRule ^([0-9]+)/([0-9]+)/([0-9]+)/(page)/([0-9]+)/?$ load.php?year=$1&month=$2&date=$3&p=$5 [L,QSA]