W = int(input())
H = int(input())
N = int(input())
SK = [list(map(int,input().split())) for _ in range(N)]
SS = set()
KS = set()
for s,k in SK:
    SS.add(s)
    KS.add(k)
NS = len(SS)
NK = len(KS)
ans = NS * H + NK * W - NS * NK - N
print(ans)