A wazir is a fairy chess piece that moves like a rook, but can go only one square.
We wish to place a number of wazirs on a 9 $\times$ 9 chessboard so the following conditions are satisfied
- Each wazir is being attacked by at least one other wazir.
- Each empty square is being attacked by at least one wazir.
What is the minimum number of wazirs we need to place to satisfy the conditions above?