Error message in calculated column

Hi,

There is a "MONTH" field in my view with values 1,2,....12 and I am trying to create a "MONTH_TXT" field from this which should show Jan for 1, Feb for 2 like that. For this I am trying to create a calculated column in calculation view as shown in the attachement.

I am trying to create this c.column in final aggregation node of c.view.Please let me know how to solve this.

Thanks,

Jyothirmayi