Instructions: This task involves annotating the answer type to a given question that involve some kind of complex reasoning (including numerical reasoning). Note that the questions require looking at more than one part of the passage to answer. There are 3 possible answer types (i) spans, (ii) numbers and (iii) dates. If the answer can be found in the passage, label it as "span". If the answer is a number, label as "number". Similarly, label "date" if you think the answer to the given question is a date.
Input: Passage: Another key development in the wake of the Forty Years' War was the emergence of a unified and powerful Arakan. The western littoral between the Arakan Yoma and the Bay of Bengal remained politically fragmented even after Pagan's fall. The coast was divided between at least two power centres at Launggyet in the north and Sandoway in the south. The weakness became exposed between 1373 and 1429 when the region was first subject first to Avan and then to Peguan interference. Arakan was Pegu's vassal from 1412 at least until Razadarit's death in 1421. The restoration came in 1429 when the last king of Arakan, Saw Mon III, in exile since 1406, came back with an army provided by Sultan Jalaluddin Muhammad Shah of Bengal. Narameikhla again became king, though as a vassal of Bengal. The vassalage was brief. In 1437, Saw Mon's brother Khayi annexed Sandoway and Ramu, his overlord's territory, unifying the Arakan littoral for the first time in history. An ascendant Arakan seized Chittagong in 1459, and received tribute from the Ganges delta.
Question: How many years was it between Saw Mon III ame back from exile and Arakan seizing Chittagong?
Output:
number