w = int(input())
h = int(input())
n = int(input())

cards = [0 for _ in range(n)]
A = set()
B = set()
for i in range(n):
    s, k = map(int, input().split())
    A.add(s)
    B.add(k)
print(w * h - (w - len(A)) * (h - len(B)) - n)