The SIS model represents an infection that does not result in immunity. In other words, there is no "recovered" population; people who have recovered re-enter the "susceptible" population. Write a difference equation for this model. Implement your difference equation using a for loop. Your model should take as parameter an initial population size, a step size dt, a number of days for the model to run, an infection rate, and a recovery rate. Assume there is one infected person to start and the rest of the population is susceptible. Your for loop should iterate int(days/dt)+1 times. End your function with the line return int(susceptible)