Calculating finished goods?

I was given the equation: ending finished goods=beginning finished goods+(direct materials+direct labor+overhead)- COGS. For DM, DL, and OH I have figures for 6 months of forcasted expenses. I was given a check figure and it's just not adding up. I have wages and salaries, manufacturing expenses, G&A expenses, interest payable, and taxes. Am I missing something? I'm thinking I'm missing something dealing with purchases. Any help would be appreciated.