The input nums is supposed to be an array of unique integers ranging from 1 to nums. Length (inclusive). However, there is a mistake: one of the numbers in the array is duplicated, which means another number is missing. Find and return the sum of the duplicated number and the missing number. Example: in the array [4, 3, 3, 1]. 3 is present twice and 2 is missing, so 3+2= 5 should be returned.