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Star Airlines serves the route between Washington, DC (National), and Portsmouth, NH, with a single flight daily. The airline sells both discount-fare and full-fare tickets. The airline has assigned a 150-seat aircraft to the flight. Using Littlewood's rule, the airline has determined that the optimal booking limit for a flight departing in two weeks is 50. The full fare for this flight is $300 and the discount fare is $100. And the mean of the full-fare demand is estimated at 80. The standard deviation of the full-fare demand for this flight is ___ (rounding to integer!), assuming that the full-fare demand follows a normal distribution.