# -*- coding: utf-8 -*-

def solve(W, H, N, S, K):
    return W * H - (W - len(set(S))) * (H - len(set(K))) - N


if __name__ == '__main__':
    W = int(raw_input())
    H = int(raw_input())
    N = int(raw_input())
    S = [0] * N
    K = [0] * N

    for n in xrange(N):
        S[n], K[n] = map(int, raw_input().split(" "))
    print solve(W, H, N, S, K)