H,W = map(int,input().split())
h,w = map(int,input().split())
TOTAL = H * W
total = (W * h + H * w)-h*w
result = TOTAL - total
print(result)
1add18d74e2e1d43bb24d68467962c5fce165080
<mask token>

<mask token>
print(result)

H, W = map(int, input().split())
h, w = map(int, input().split())
TOTAL = H * W
total = W * h + H * w - h * w
result = TOTAL - total
print(result)

H,W = map(int,input().split())
h,w = map(int,input().split())
TOTAL = H * W
total = (W * h + H * w)-h*w
result = TOTAL - total
print(result)