Problem with subtracting

I'm new to this so bare with me... I'm tying to make a label decrease in a number but I keep getting errors when I try to.

The codes are part of a timer, the error is in the 4th line of this:

            int y = 1;
            string n = "60";
            label1.Text = n;
            label1 = label1.Text - y;

That's my most recent attempt, can anyone tell me what its suppose to be?