Title: Bulgaria–Romania border
Content:  The Bulgaria–Romania border (Граница между България и Румъния, Frontiera între Bulgaria și România) is the state border between Bulgaria and Romania. For most of its length, the border follows the course of the lower Danube, up until the town of Silistra. From Silistra, the river continues north into the Romanian territory. East of that point, the land border passes through the historical region of Dobruja, dividing it into Northern Dobruja in Romania and Southern Dobruja in Bulgaria. The Bulgaria–Romania border is an internal border of the European Union. However, as of 2022 neither country is part of the Schengen Area. As a result, border controls are conducted between the two countries, albeit often jointly (once per crossing).
Title: Geography of Romania
Content: total: 3,149.9 km (1,957.2 mi) ; border countries: Bulgaria 631 km (382 mi), Hungary 448 km (278 mi), Moldova 681 km (423 mi), Serbia 546 km (339 mi), and Ukraine to the north and east for 649 km (403 mi). 
Title: Romania–Russia relations
Content:   Romania–Russia relations are the foreign relations between Romania and Russia. Romania has an embassy in Moscow and consulates-general in Rostov-on-Don and Saint Petersburg. Russia has an embassy in Bucharest and a consulate-general in Constanţa. Historical relations have oscillated among grudging cooperation, neutrality, open hatred and hostility. Both countries refused to recognize Kosovo's declaration of independence from Serbia and strongly supported its territorial integrity. About 30,000 Russians live in Romania, mainly in the Tulcea County (see Lipovans). About 5,308 Romanians live in Russia, mainly in the Russian Far East. Both countries are full members of the Council of Europe and the Organization for Security and Co-operation in Europe. In 1992 and 1993, relations between 
Title: Belarus–Russia border
Content:  The Russian-Belarusian border is the state border between Russia and Belarus. Prior to 1991, it was the border between the Russian Soviet Federative Socialist Republic and the Byelorussian Soviet Socialist Republic. The border formally exists, but is not subject to customs checks or duty due to the Union State treaty and the Eurasian Union. The length of the border is 1239 km, including 857.7 km of land, 362.3 km of river and 19 km of lake.
Title: Geography of Romania
Content:   With an area of 238,397 km2, Romania is the twelfth-largest country in Europe. Located in Southeastern Europe, bordering on the Black Sea, the country is halfway between the equator and the North Pole and equidistant from the westernmost part of Europe—the Atlantic Coast—and the most easterly—the Ural Mountains. Romania has 3,195 km of border. Republic of Moldova and Ukraine lie to the east, Bulgaria lies to the south, and Serbia and Hungary to the west. In the southeast, 245 km of sea coastline provide an important outlet to the Black Sea and the Atlantic Ocean.
Title: Romania–Ukraine border
Content:  The land border consists of two parts: the northern part stretches across Carpathian Mountains region roughly west–east from the Hungary-Romania-Ukraine tripoint to the northern Moldova-Romania-Ukraine tripoint. It starts along the Tisza River (through Maramureș) and runs across the historical region of Bukovina in the Eastern Carpathians. The southern part stretches between Budjak and Dobrudja regions roughly west–east from the southern Moldova-Romania-Ukraine tripoint to the maritime Romania-Ukraine boundary. It runs along the Danube River, its Chilia branch (most northern branch) of its delta to the Black Sea. Until Soviet occupation of Bessarabia and Northern Bukovina, Dniester (Nistru) river used to serve as international border between Ukraine (later the Ukrainian SSR) and Romania.
Title: Bulgaria–Romania relations
Content:  Bulgarian-Romanian relations are foreign relations between Bulgaria and Romania. Bulgaria has an embassy in Bucharest. Romania has an embassy in Sofia and three honorary consulates (in Burgas, Silistra and Vidin). There are 7,336 Bulgarians who are living in Romania and around 4,575 Romanians living in Bulgaria. The countries share 608 km of common borders, mostly along the Danube.
Title: Belarus–Romania relations
Content:  Belarus–Romania relations are the foreign relations between Belarus and Romania. Currently, Belarus has an embassy in Bucharest, while Romania has an embassy in Minsk. Both countries officially established diplomatic relations on 14 February 1992.
Title: Romania–Ukraine border
Content:   The Romania–Ukraine border is the state border between Romania and Ukraine. It consists of both a land and a maritime boundary. The total border length is 613.8 km including 292.2 km by rivers and 33 km by the Black Sea. It is part of the external border of the European Union (since Romania's accession to the EU in January 2007). For the maritime part, see Maritime Delimitation in the Black Sea case.
Title: Geography of Lithuania
Content:  two countries share a border that extends 453 kilometres. Lithuania's eastern border with Belarus is longer, stretching 502 kilometers. The border with Poland on the south is relatively short, only 91 kilometers, but it is very busy because of international traffic. Lithuania also has a 227-kilometer border with Russia. Russian territory adjacent to Lithuania is Kaliningrad Oblast, which is the northern part of the former German East Prussia, including the city of Kaliningrad. Finally, Lithuania has 108 kilometers of Baltic seashore with an ice-free harbor at Klaipėda. The Baltic coast offers sandy beaches and pine forests and attracts thousands of vacationers.

Question: what country shares borders with both belarus and romania?
Answer: Ukraine.