Period	Forecast
1	200
2	500
3	300
4	400
5	200
6	200

Regular time: $20 per unit (maximum of 280 units per period)

Overtime: $30 per unit (maximum of 40 units per period)

Subcontracting: Not available

Beginning inventory: None

Carrying cost: $10 per unit per period

Backorder cost: $50 per unit per period

What is the first period in which overtime should be scheduled in order to minimize total cost for the aggregate plan?