Answer:
Romania
Step-by-step explanation:
Going to the east , we find Hungary's natural neighbour :Romania.
The border between this lands dates to 1920 by an international commission. The border was set by the Treaty of Trianon which was signed on 4 June 1920.
The border stretches 448 km long, demarcated by pillars and about 20 km of the Mureș River. Relations between Hungary and Romania are relatively stable. Often conflicts between alleged borders arise in the surrounding countries like Ukraine and Serbia. Fortunately the border
between Hungary–Romania border is an internal border of the European Union. As of 2019, Romania is not a member of the Schengen Area.