xy-x-y+1=3
(x-1)(y-1)=3
x-1=1,y-1=3
x=2,y=4
x-1=3,y-1=1
x=4,y=2
x-1=-1,y-1=-3
x=0,y=-2
x-1=-3,y-1=-1
x=-2,y=0