points = ((1, 2), (3, 4), (5, 4))
area = 0.0
for i, j in zip(points[:-1], points[1:]):
    area += (j[0] - i[0]) * (i[1] + j[1]) / 2.0
width = points[-1][0] - points[0][0]
average = area / width
print average