W = int(input())
H = int(input())
N = int(input())
marks = set()
nums =  set()
for n in range(N):
    S, K = map(int, input().split())
    marks.add(S)
    nums.add(K)
len_marks = len(marks)
len_nums = len(nums)
count = len_marks * H + len_nums * W - len_marks * len_nums - N
print(count)