#!/usr/bin/env python3

x1 = int(input())
y1 = int(input())
x2 = int(input())
y2 = int(input())

total = (x2 - x1) * (y2 - y1)

print(total)

#!/usr/bin/env python3

x1 = int(input())
y1 = int(input())
x2 = int(input())
y2 = int(input())

total = (x2 - x1) * (y2 - y1)

print(total)

#!/usr/bin/env python3