W,H,N = int(raw_input()),int(raw_input()),int(raw_input())
S,K = [0 for i in range(N)],[0 for i in range(N)]
nm = [[0 for j in range(H)]for i in range(W)]
for i in range(N):
	S[i],K[i] = map(int,raw_input().split())
	nm[S[i] - 1][K[i] - 1] = - 1
	for j in range(W):
		if nm[j][K[i] - 1] >= 0:
			nm[j][K[i] - 1] += 1
	for j in range(H):
		if nm[S[i] - 1][j] >= 0:
			nm[S[i] - 1][j] += 1
count = 0
for i in range(W):
	for j in range(H):
		if nm[i][j] >= 1:
			count += 1
print count