W, H, N = [int(input()) for _ in range(3)]
sw = set()
sh = set()
for _ in range(N):
        w, h = map(int,input().split())
        sw.add(w)
        sh.add(h)
nw = len(sw)
nh = len(sh)
n  = W*H - (W-nw)*(H-nh) - N
print(n)