Instructions: This task involves creating answers to complex questions, from a given passage. Answering these questions, typically involve understanding multiple sentences. Make sure that your answer has the same type as the "answer type" mentioned in input. The provided "answer type" can be of any of the following types: "span", "date", "number". A "span" answer is a continuous phrase taken directly from the passage or question. You can directly copy-paste the text from the passage or the question for span type answers. If you find multiple spans, please add them all as a comma separated list. Please restrict each span to five words. A "number" type answer can include a digit specifying an actual value. For "date" type answers, use DD MM YYYY format e.g. 11 Jan 1992. If full date is not available in the passage you can write partial date such as 1992 or Jan 1992. If you find multiple spans, please add them all as a comma separated list. Please restrict each span to five words.
Input: Passage: The earliest human remains found on the island of Sri Lanka date to about 35,000 years ago . The proto-historical period begins roughly in the 3rd century, based on chronicles like the Mahavamsa, Dipavamsa, and the Culavamsa. The earliest documents of settlement in the Island are found in these chronicles. These chronicles cover the period since the establishment of the Kingdom of Tambapanni in the 6th century BCE. The first Sri Lankan ruler of the Anuradhapura Kingdom, Pandukabhaya, is recorded for the 4th century BCE. Buddhism was introduced in the 3rd century BCE by Arhath Mahinda . The first Tamil ruler of the Anuradhapura Kingdom, Ellalan, an invader, is recorded for the 2nd century BCE. The island was divided into numerous kingdoms over the following centuries, intermittently united under Chola rule. Sri Lanka was ruled by 181 monarchs from the Anuradhapura to Kandy periods.From the 16th century, some coastal areas of the country were also controlled by the Portuguese, Dutch and British.Between 1597 and 1658, a substantial part of the island was under Portuguese rule. The Portuguese lost their possessions in Ceylon due to Dutch intervention in the Eighty Years' War. Following the Kandyan Wars, the island was united under British rule in 1815.Armed uprisings against the British took place in the 1818 Uva Rebellion and the 1848 Matale Rebellion. Independence was finally granted in 1948 but the country remained a Dominion of the British Empire until 1972. In 1972 Sri Lanka assumed the status of a Republic. A constitution was introduced in 1978 which made the Executive President the head of state. The Sri Lankan Civil War began in 1983, including an armed youth uprising in 1971 and 1987-1989, with the 25-year-long civil war ending in 2009.
Question: How many years apart was the the two armed youth uprising in 1971 and 1987>?
Answer type: Number
Output:
16.