How do I convert a string to an int type in C#?

I am taking a string value from a textbox named txtLastAppointmentNo and I want to convert it to an int and then store it in a database using Linq to sql but I am getting error "input string was not in proper format".

My input string is 2.

My code is:

      objnew.lastAppointmentNo=Convert.ToInt32(txtLastAppointmenNo.Text);

Please point out my mistake.