public class CustomMaskedCurrencyInput : RadMaskedCurrencyInput
{
	protected override void HandlePaste()
	{
		object clipBoardValue = Clipboard.GetText();
		if (clipboardValue can be parsed to a number and it is a negative number)
		{
			// don't call the base method
		}
		else 
		{
			base.HandlePaste();
		}
	}
}