How make automatical resize (downscaling) with avs?

[Dreamject]

I'm newbe, do not hit me)

I wanna make something like downscaling to, for example, 1366/768 display

So
1) Resizing should works only as downscaling
2) Target width/height should be devided to 2 without float (resizing limitation at least in SVP)

Ideally it should be like
TargetRes="1366,768"
But
TargetWidth=1366
TargetHeight=768
is okay too

I'm not familiar with avisynth, imho it should be like

WidthDen=width/TargetWidth
HeightDen=height/TargetHeight

WidthDen OR HeightDen > 1 eval("""
WidthDen > HeightDen eval("""
cropstring="BicubicResize(round(width/WidthDen),round(height/WidthDen),b=0,c=0.75)"
""") : eval ("""
cropstring="BicubicResize(round(width/HeightDen),round(height/HeightDen),b=0,c=0.75)"
""") : cropstring=""

But them also should be rounded to bigger number than must be devided to 2