# Input
W = int(input())
H = int(input())
N = int(input())
S = [ None ] * N
K = [ None ] * N
for i in range(N):
	S[i], K[i] = map(int, input().split())

# Calculation
A = len(set(S))
B = len(set(K))
print(W * H - (W - A) * (H - B) - N)