Bob's Fly cataiog collected forecasts, sales, and demand data for $20$ items in one category from its previous catalog. The data is provided below in the table.For example, their forecast for the first item in the table was $100$ units, but it unfortunately only sold $26$ units. However, with the last item listed, they sold $341$ units but could have sold $569$ units if they had ordered enough inventory. For the next cataiog, they have an item for which they forecast demand to bo $360$ units. Suppose they will use that forecast along with the data in the above table to choose a normal distribution to model demand for this product. What standard deviation should they choose? $($Keep the answer as an inveger.$)$