x1 = int(input())
y1 = int(input())
x2 = int(input())
y2 = int(input())
x3 = int(input())
y3 = int(input())
x4 = int(input())
y4 = int(input())

x5 = max(x1, x3)
y5 = max(y1, y3)
x6 = min(x2, x4)
y6 = min(y2, y4)

if x5 >= x6 or y5 >= y6: S = 0
else: S = (x6 - x5) * (y6 - y5)
print(S)