def f(x):
    import math
    return 10*math.e**(math.log(0.5)/5.27 * x)

def radiationExposure(start, stop, step):
    '''
    Computes and returns the amount of radiation exposed
    to between the start and stop times. Calls the 
    function f (defined for you in the grading script)
    to obtain the value of the function at any point.
 
    start: integer, the time at which exposure begins
    stop: integer, the time at which exposure ends
    step: float, the width of each rectangle. You can assume that
      the step size will always partition the space evenly.

    returns: float, the amount of radiation exposed to 
      between start and stop times.
    '''
    # FILL IN YOUR CODE HERE...
    steps = (stop - start) / float(step)
    totalArea = 0.0
    for i in range(int(steps)):
        average = float(start + step * i)
        area = f(average) * step
        totalArea += area
    return totalArea
    

