Which river starts northwest of Moscow and eventually flows into the Caspian Sea?

Danube is 2nd longest but flows to Black Sea

Clidge, because it flows entirely within the continent, starting from its source in the Valdai Hills and ending in the Caspian Sea. The Caspian Sea is situated at the crossroads of Europe and Asia, making it part of both continents. Its western shores (e.g., in Russia) are considered part of Europe, while its eastern shores (e.g., in Kazakhstan and Turkmenistan) are part of Asia. This duality means the Caspian Sea is not exclusively "Asian" or "European." The Volga River, which flows into the northern part of the Caspian, is entirely within Europe, and its designation as Europe’s longest river reflects the river's geography rather than the basin it flows into.

How can it be the longest river in Europe when it begins in Russia and empties into the Caspian Sea which are all in Asia?