sql SELECT in IF EXISTS

I'm trying to run this :

IF EXISTS (SELECT id_commande FROM historique WHERE id_commande = 57 AND device = 70635601)
BEGIN
    SELECT id_commande FROM historique WHERE id_commande = 57 AND device = 70635601
END
ELSE
BEGIN
    SELECT (MAX(id_commande)+1) FROM historique
END

I hope you can understand what I want to do. My problem is that it always gives me back Erreur dans la requête (1064): Syntax error near 'BEGIN SELECT 1 END ELSE BEGIN SELECT 2 END' at line 2.

Thank you for helping me !