w = int(input())
h = int(input())
n = int(input())

suits = set()
numbers = set()

for _ in range(n):
    s, k = map(int, input().split())
    suits.add(s)
    numbers.add(k)

s_count = len(suits)
k_count = len(numbers)

a = s_count * h + k_count * w - s_count * k_count
print(a - n)