w = int(input())
h = int(input())
n = int(input())
set_s = set()
set_k = set()
 
for i in range(n):
    s, k = map(int, input().split())
    set_s.add(s)
    set_k.add(k)
 
len_s = len(set_s)
len_k = len(set_k)
ans = len_s * h + len_k * w - len_s * len_k - n
 
print(ans)