Mask of mask Text box fro decimal

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WPF

WPF-Toolkit

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i am using masked text box i want the mask textbox to take max 7 digits and two decimals.
for e.g 1234567.12.Currently i use mask as "dddddddddd".in my table the decimal precision is 9,2.so the user can able to put 8 digits so the arithmatic overflow exception is coming.
can anybody suggest mask for this situation.i have also tried with ddddddd.dd but this is also not worked for me.

MaskedTextBox x:Name="TxtTransPort"
                                       Grid.Row="1"
                                       Width="78"
                                       Height="23"
                                       Margin="142,161,0,0"
                                       HorizontalAlignment="Left"
                                       VerticalAlignment="Top"
                                       AllowSign="False"
                                       GroupNumerals="True"
                                       InputMask="ddddddd"
                                       IsEnabled="False"
                                       PromptChar=" "
                                       TextAlignment="Right"
                                       GotFocus ="TextBox_GotFocus"/>