Conflict, What is the right htaccess rule, default homepage file with htaccess?

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usually i use this htaccess rule to define default homepage file

RewriteRule ^$ forum.php

but in one of my website, above rule is conflict with the other htaccess

RewriteRule ^{((archive/)?(..php(/.)?)?)$} blog.php [L,QSA]

so the first rule is not working

please help how is the correct rule so both rule not conflict (maybe joining or split them)

i must found the answer, please help guys