w = int(input())
h = int(input())
n = int(input())
L = [tuple(map(int,input().split())) for i in range(n)]
sW = set()
sH = set()
for x,y in L:
    sW.add(x)
    sH.add(y)

ans = h*w
ans -= len(sW)*h+len(sH)*w-len(sW)*len(sH)
print(h*w-ans-n)