118- The natural numbers are grouped in such a way that the number of members in each group (except the first and second groups) equals the sum of the members of the two preceding groups; that is: $\ldots, \{11, 12\}, \{7, 8, 9, 10\}, \{4, 5, 6\}, \{2, 3\}, \{1\}$. What is the average of the members of the thirteenth group?
(1) $2204.5$ (2) $3072.5$ (3) $4350.5$ (4) $6144.5$