In the cells of a $5 \times 5$ grid there are some lamps. If a lamp is touched, it is turned on and it lights up all of its neighbouring cells, including its own cell. If a cell is lit up and there is a lamp in it, the lamp is also turned on and lights up its neighbouring cells, including its own. What is the smallest number of lamps needed to light up all of the cells with just one touch? (Note: Two cells are neighbours if they have a common side or vertex.)