Please refer to the following code snippet:

        public Form1()
        {
            InitializeComponent();
             
            this.radMaskedEditBox1.Mask = "n";
            this.radMaskedEditBox1.MaskType = Telerik.WinControls.UI.MaskType.Numeric;   
            this.radMaskedEditBox1.Culture = new CultureInfo("en-CA") { NumberFormat = { NumberDecimalDigits = 0, NumberGroupSeparator = "," } };  
        }

After running the application and try to enter "123". You will notice that you can enter only "1".