[H, W] = list(map(int, input().split()))
[X, Y] = list(map(int, input().split()))
print((H - X) * (W - Y))

2fc54afd15f2fadf2559b28875e059de2d383aa9
<mask token>

<mask token>
print((H - X) * (W - Y))

[H, W] = list(map(int, input().split()))
[X, Y] = list(map(int, input().split()))
print((H - X) * (W - Y))
