w=int(input())
h=int(input())
n=int(input())
SK=[list(map(int,input().split())) for _ in range(n)]

SK.sort()
wsum,hsum=1,1
for i in range(1,n):
    if SK[i-1][0]!=SK[i][0]:
        wsum+=1
    if SK[i-1][1]!=SK[i][1]:
        hsum+=1
print((w*h) - (w-wsum)*(h-hsum) - n)