Consider the following instance of the knapsack problem :
$\begin{array}{|c|c|c|c|c|c|} \hline \text{Item} & a & b & c & d & e \\ \hline \text{Benefit} & 15 & 12 & 9 & 16 & 17 \\ \hline \text{Weight} & 2 & 5 & 3 & 4 & 6 \\ \hline \end{array}$
Maximum weight of knapsack is $12$. For the above weights and benefits of items, if we need an optimal solution of fractional knapsack problem, the value of maximum benefit will be ______.