Question: What is the capital city of the least populous nation where Himalayan Butterfly Bush grows?

Context paragraphs:
Himalayan University: Himalayan University is a UGC, Government of India recognised University in India established in 2013 by the Government of Arunachal Pradesh, located at the Nahalargun in the Regional Capital Itanagar.  The Himalayan University is accredited and recognised by the University Grants Commission under the constitutional law, section of 2 f of UGC act 1956.  With its introduction to Arunachal Pradesh, regional capital city Itanagar has now tagged with Himalayan University where students will find a wide range of degree programmes at under graduate, post graduate and doctoral levels and Post Doctoral Research Programme with Full scholarship, partial scholarship, sponsorship availability to eligible candidates.  The "Arunachal Pradesh Gazette" too approved the segment of Himalayan University under state government approval act no 6 of 2012.

Grano, North Dakota: Grano is a city in Renville County, North Dakota, United States.  The population was seven at the 2010 Census, tying Bergen as the second least populous incorporated place in North Dakota (Ruso was the least populous).

Ethiopia: Ethiopia ( ; Amharic: , "ʾĪtyōṗṗyā ",    ), officially the Federal Democratic Republic of Ethiopia (የኢትዮጵያ ፌዴራላዊ ዲሞክራሲያዊ ሪፐብሊክ, "yeʾĪtiyoṗṗya Fēdēralawī Dēmokirasīyawī Rīpebilīk"    ), is a country located in the Horn of Africa.  It shares borders with Eritrea to the north and northeast, Djibouti and Somalia to the east, Sudan and South Sudan to the west, and Kenya to the south.  With over 100 million inhabitants, Ethiopia is the most populous landlocked country in the world, as well as the second-most populous nation on the African continent.  It occupies a total area of 1,100,000 km2 , and its capital and largest city is Addis Ababa.

Helena, Montana: Helena is the capital city of the U.S. state of Montana and the county seat of Lewis and Clark County.  As of the 2010 census the population at 28,190, making it the fifth least populous state capital in the U.S.  It was founded as a gold camp during the Montana gold rush, and was established in 1864.  Over $3.6 billion of gold was extracted in the city limits over a duration of two decades, making it one of the wealthiest cities in the United States by the late nineteenth century.  The concentration of wealth contributed to the city's prominent, elaborate Victorian architecture.

Ngerulmud: Ngerulmud is the seat of government of the Republic of Palau, an island nation in the Pacific Ocean.  It replaced Koror City, Palau's largest city, as capital in 2006.  The settlement is located in the state of Melekeok on Babeldaob, the country's largest island, located 20 km northeast of Koror and 2 km northwest of Melekeok City.  It is the world's least populous capital of a sovereign state.

Buddleja crispa: Buddleja crispa, sometimes called the Himalayan Butterfly Bush, is native to Afghanistan, Bhutan, North India, Nepal, Pakistan and China (Gansu, Sichuan, Xizang), where it grows on dry river beds, slopes with boulders, exposed cliffs, and in thickets, at elevations of 1400–4300 m.

Montpelier, Vermont: Montpelier is the capital city of the U.S. state of Vermont and the seat of Washington County.  As the site of Vermont's state government, it is the least populous state capital in the United States.  The population was 7,855 at the 2010 census.  However, the daytime population swells to about 21,000, due to the large number of jobs within city limits.  The Vermont College of Fine Arts and New England Culinary Institute are located in the municipality.  It was named for Montpellier, in southern France.

Nauhatta Block: Nauhatta Block with population of about 1.6 lakh is Saharsa district's the 5th least populous sub district, located in Saharsa district of the state Bihar in India.  There are 58 villages in the sub district, among them Nauhatta is the most populous village with population of about 25 thousand and Balugaon urf Chhatra is the least populous village with population of 189.  Nauhatta is the biggest village in the sub district with an area of 21 km2.  Nauhatta Block Headquarters is Nauhatta town.  It belongs to Kosi Division .  It is located 21 km towards North from District headquarters Saharsa and 167 km from State capital Patna towards west.

List of companies of Ethiopia: Ethiopia is a country located in the Horn of Africa.  It shares borders with Eritrea to the north and northeast, Djibouti and Somalia to the east, Sudan and South Sudan to the west, and Kenya to the south.  With nearly 100 million inhabitants, Ethiopia is the most populous landlocked country in the world, as well as the second-most populous nation on the African continent after Nigeria.  It occupies a total area of 1,100,000 km2 , and its capital and largest city is Addis Ababa.

Bhutan: Bhutan ( ; འབྲུག་ཡུལ་ "druk yul "), officially the Kingdom of Bhutan (འབྲུག་རྒྱལ་ཁབ་ "druk gyal khap "), is a landlocked country in South Asia.  Located in the Eastern Himalayas, it is bordered by Tibet Autonomous Region in the north, India in the south, the Sikkim state of India and the Chumbi Valley of Tibet in the west, and Arunachal Pradesh state of India in the east.  Bhutan is geopolitically in South Asia and is the region's second least populous nation after the Maldives.  Thimphu is its capital and largest city, while Phuntsholing is its financial center.

Supporting paragraphs: Buddleja crispa Bhutan
Answer: Thimphu