Dim pux As Double = Parameter("PU_X")
Dim puy As Double = Parameter("PU_Y")

Dim a As Double
Dim b As Double

If pux > puy Then
    a = pux
    b = puy
Else
    a = puy
    b = pux
End If
iProperties.Value("Custom", "IU_X") = a
iProperties.Value("Custom", "IU_Y") = b