Wood&Foster Electronics is planning the production of its latest tablet model, "TabX Ultra," for the next $6$ months. The company is planning to run production only twice, in Month $1$ and Month $4.$ Each production run should cover the demand for that month and the subsequent months until the next production, while maintaining a minimum inventory of $900$ units at the end of each month, including Month $6.$

The forecasted demand for TabX Ultra tablets over the next $6$ months is as follows: