write (*,*) 'Enter x0,y0:'
        read (*,*) x0,y0
        write (*,*) 'Enter a:'
        read (*,*) aa
c----node 1----
        a=aa/2.-x0
        b=-aa/2.-y0
        ang1=angle(a,b)*180./3.14159
        write (*,*) ang1
c----node 2----
        a=aa/2.-x0
        b=aa/2.-y0
        ang2=angle(a,b)*180./3.14159
        write (*,*) ang2
c----node 3----
        a=-aa/2.-x0
        b=aa/2.-y0
        ang3=angle(a,b)*180./3.14159
        write (*,*) ang3
c----node 4----
        a=-aa/2.-x0
        b=-aa/2.-y0
        ang4=angle(a,b)*180./3.14159
        write (*,*) ang4
        stop
        end


        real function angle(a,b)
        pi=3.141593
        if(a.eq.0.0)then
          if(b.gt.0.0)angle=0.5*pi
          if(b.lt.0.0)angle=1.5*pi
        else if(a.lt.0.0)then
          angle=pi+atan(b/a)
        else
          angle=atan(b/a)
          if(b.lt.0.0)angle=angle+2.*pi
        endif
        return
        end