Write a function named between_endpoints that accepts a list of integers and returns how many of its entries are strictly between the first and the last entry. For example, given [1, 2, 1, 3] you would return 1 because only one entry (2) is between the first and last entries (1 and 3). Note that the bigger endpoint could either the first or the last entry. Assume that the list has at least 2 entries.