mysql trigger error when declaration : i try to create a trigger but i get this error after execute the SQL;

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'DECLARE temp INT' at line 4

here is my trigger

CREATE TRIGGER hesap 

AFTER INSERT ON uber  

 DECLARE temp INT;

 BEGIN    IF uber.il='ANKARA' THEN 
  temp=5+(uber.mesafe*0.5);  

 ELSEIF uber.il='ISTANBUL' THEN  
 temp=10+(uber.mesafe*0.5);   

ELSEIF uber.il='IZMIR' THEN  
 temp=3+(uber.mesafe*0.5);  

 END IF; 
     
INSERT INTO fatura VALUES(uber.uid,temp)

END;