The green line is the directrix x+y+1 = 0



The vertex V is half-way between the focus and the directrix on
a perpendicular from the focus to the directrix, the blue line
below:



Draw perpendiculars from the end of that blue line and from 
the vertex V to the x-axis:



Now with a little bit of geometry knowledge, it's easy to 
see that the vertex is 

Edwin