w = int(input())
h = int(input())
n = int(input())
s = []
k = []
for _ in range(n):
    i, j = map(int,input().split())
    s.append(i)
    k.append(j)

s = list(set(s))
k = list(set(k))

x = len(s)
y = len(k)
z = w*h - ((w-x)*(h-y)) - n

print(z)