The Prime Minister of India (IAST: ) is the head of government of the Republic of India. Executive authority is vested in the prime minister and their chosen Council of Ministers, despite the president of India being the nominal head of the executive. The prime minister is often the leader of the party or the coalition with a majority in the lower house of the Parliament of India, the Lok Sabha, which is the main legislative body in the Republic of India. The prime minister and their cabinet are at all times responsible to the Lok Sabha. The prime minister is appointed by the president of India; however the prime minister has to enjoy the confidence of the majority of Lok Sabha members, who are directly elected every five years, lest the prime minister shall resign. The prime minister can be a member of the Lok Sabha or of the Rajya Sabha, the upper house of the parliament. The prime minister controls the selection and dismissal of members of the Union Council of Ministers; and allocation of posts to members within the government. The longest-serving prime minister was Jawaharlal Nehru, also the first prime minister, whose tenure lasted 16 years and 286 days. His premiership was followed by Lal Bahadur Shastri's short tenure and Indira Gandhi's 11- and 4-year-long tenures, both politicians belonging to the Indian National Congress. After Indira Gandhi's assassination, her son Rajiv Gandhi took charge until 1989, when a decade with six unstable governments began. This was followed by the full terms of Atal Bihari Vajpayee, Manmohan Singh, and Narendra Modi. Modi is the 14th and current prime minister of India, serving since 26 May 2014. Origins and history India follows a parliamentary system in which the prime minister is the presiding head of the government and chief of the executive of the government. In such systems, the head of state, or, the head of state's official representative (i.e., the monarch, president, or governor-general) usually holds a purely ceremonial position and acts—on most matters—only on the advice of the prime minister. The prime minister—if they are not already—must become a member of parliament within six months of beginning his/her tenure. A prime minister is expected to work with other central ministers to ensure the passage of bills by the parliament. 1947–1984 Since 1947, there have been 14 different prime ministers. The first few decades after 1947 saw