How to assign the drop down value based on the Text value of another column in sharepoint 2010?

I have created a custom list in sharepoint 2010 which contains two columns.

One column is single line of text.

Second column is dropdown which contains 4 values (q1,q2,q3,q4).

if the text of first column contains as( jan or Feb or Mar) the dropdown should automatically select as q1.

if the text of first column contains as( Apr or may or jun) the dropdown should automatically selected as q2.

if the text of first column contains as( jul or Aug or Sep) the dropdown should automatically select as q3.

if the text of first column contains as( Oct or nov or dec) the dropdown should automatically select as q4.

How can achieve this requirement?

Please help.

Thanks in advance