W = int(input())
H = int(input())
N = int(input())
S = set()
K = set()
for _ in range(N):
    s,k = map(int,input().split())
    S.add(s)
    K.add(k)
ans = len(S)*H+len(K)*W-2*N-(len(S)*len(K)-N)
print(ans)