Correct Syntax Using Variables Inside SQL Queries (SqlCommand)

I have a test page where I'm using SqlConnection and SqlCommand to update a simple database table (decrease a number).

I'm trying to figure out how to make a number in the database table to decrease by 1 each time a button is being pressed. I know how to update the number by whatever I want to, but I have no idea what the correct syntax is for putting variables inside the query etc. Like "count -1" for instance.

The database table is called "friday" and the one and only column is called "Tickets".

Here's the code behind the button:protected void Button1_Click(object sender, EventArgs e)

{SqlConnection conn;

conn = new SqlConnection("Data Source=***;Initial Catalog=***;Persist Security Info=True;User ID=***;Password=***");

conn.Open();int count = -1;

 SqlCommand cmd = new SqlCommand("select Tickets from friday", conn);

count = (int)cmd.ExecuteScalar();if (count > 0)

{

 string updateString = @"

update friday

set Tickets = 500" ;   <------ Here I want to set Tickets like "current count -1"SqlCommand cmd2 = new SqlCommand(updateString);

cmd2.Connection = conn;

cmd2.ExecuteNonQuery();

}

else

{

}

conn.Close();

}