Sum Neighbors until Two Numbers Left

Given a list of integers, repeatedly sum adjacent pairs and take the last digit (i.e., modulo 10) until only two numbers remain in the list. Return these two numbers as a concatenated string. Example Input: [1, 2, 3, 4] Output: '82' Explanation [1, 2, 3, 4] -> [3, 5, 7] [3, 5, 7] -> [8, 2] Finally, output '82'. Example Input [1, 2, 3, 4]