Cheapest Office

There is a tech park, which consists of $N$ rooms, numbered $1, 2, \ldots, N$. The $i$-th room has a cost of $A_i$ associated with it. There are $M$ bi-directional passages between these rooms. Chef wants to create an office in this tech park, for which she will select exactly $K$ out of these $N$ rooms. These $K$ rooms must be selected such that every selected room is reachable from every other