Addition operating at a SQL query?

Question

Hello,
I just wanna do a simple operation. My sql query is below;

UPDATE IP_KONTROL SET up_down= '" + rdr["up_down"] + 1 + "'   WHERE spe = '" + specif + "' ", conn

I just want to increase rdr's value 1, and Update it. I mean I want to increase rdr["up_down"]'s value. But it isnt adding +1. For example if rdr["up_dow"]'s value is 2, and then it is updating "21".. It should be "3", not "21".  How can i do that?