Inserting concatenate Identity column with other column

I have a identity column and i have other column while inserting a new row in 
 table i need to insert into third column with concatenate of two columns result 

For reference please see below table

------------------------------------------------
 A    |   B   |  c  
----------------------------------------------
 1    |  33   |   133(1 [identity result] + 33)    
 2    |  112  |   2112

Please help me to solve this issue.