What one of the following cities is not a capital located on Danube river?

The city that is not a capital located on the Danube River is Vienna. While Vienna is indeed the capital of Austria and located on the Danube, other cities like Budapest (Hungary), Bratislava (Slovakia), and Belgrade (Serbia) are also capitals situated along the river. However, if considering other major cities such as Prague, which is not a capital city on the Danube, it would also fit this description.