import sys

sys.setrecursionlimit(10 ** 8)

input = sys.stdin.readline


def main():
    W = int(input())
    H = int(input())
    N = int(input())
    SK = [[int(x) for x in input().split()] for _ in range(N)]

    sets = set()
    setk = set()
    for s, k in SK:
        sets.add(s)
        setk.add(k)

    ans = len(sets) * H + len(setk) * W - len(sets) * len(setk) - N
    print(ans)





    

if __name__ == '__main__':
    main()