func main()
	var px: int :: cui@inputInt()
	var py: int :: cui@inputInt()
	var qx: int :: cui@inputInt()
	var qy: int :: cui@inputInt()
	
	var ans: float :: ((px - qx).abs() + (py - qy).abs()) $ float / 2.0
	do cui@print("\{ans}\n")
end func