import sys

def input(): return sys.stdin.readline().strip()
def list2d(a, b, c): return [[c] * b for i in range(a)]
def list3d(a, b, c, d): return [[[d] * c for j in range(b)] for i in range(a)]
def list4d(a, b, c, d, e): return [[[[e] * d for j in range(c)] for j in range(b)] for i in range(a)]
def ceil(x, y=1): return int(-(-x // y))
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(N=None): return list(MAP()) if N is None else [INT() for i in range(N)]
def Yes(): print('Yes')
def No(): print('No')
def YES(): print('YES')
def NO(): print('NO')
sys.setrecursionlimit(10 ** 9)
INF = 10 ** 19
MOD = 1000003
EPS = 10 ** -10

W = INT()
H = INT()
N = INT()
have = list2d(H, W, 0)
row = [0] * H
col = [0] * W
for i in range(N):
    s, k = MAP()
    s -= 1; k -= 1
    have[k][s] = 1
    row[k] = 1
    col[s] = 1

ans = 0
for i in range(H):
    for j in range(W):
        if not have[i][j] and (row[i] or col[j]):
            ans += 1
print(ans)