Given a multiset of integers, find the subset of integers that adds to the maximum sum, such that no two numerically consecutive integers (i.e., n and n+1) are in the subset. Return the maximum sum.

INPUT: {1, 1, 1, 2, 2, 3, 6}
OUTPUT: 12
EXPLANATION: Take the 1's, 3's, and 6's:   1+1+1+3+6 = 12