import sys
import io, os
input = io.BytesIO(os.read(0,os.fstat(0).st_size)).readline

w = int(input())
h = int(input())
n = int(input())
S = set()
K = set()
for i in range(n):
    s, k = map(int, input().split())
    S.add(s)
    K.add(k)
a = len(S)
b = len(K)
ans = h*w-(w-a)*(h-b)-n
print(ans)