Assume that production required in periods 1, 2 and 3 respectively are 1,200, 1,500, and 900 units. One worker during the planning horizon can produce two units in one day. Number of workdays are 22 in period 1, 17 in period 2, and 21 in period 3. Assume that the beginning inventory and the ending inventory required are 300 units each. 

What is the number of workers required during the planning horizon of three periods?