Opinion of the European Central Bank of 6 July 2006 at the request of the Council of the European Union on a proposal for a Council Regulation amending Regulation (EC) No 974/98 on the introduction of the euro and on a proposal for a Council Regulation amending Regulation (EC) No 2866/98 on the conversion rates between the euro and the currencies of the Member States adopting the euro (CON/2006/36)