import sys

input = sys.stdin.readline


def main():
    W = int(input())
    H = int(input())
    N = int(input())

    ss = set()
    sk = set()
    for i in range(N):
        S, K = map(int, input().split())
        ss.add(S)
        sk.add(K)

    print(W*len(sk) + H*len(ss) - len(sk)*len(ss) - N)


if __name__ == '__main__':
    main()