mod = 1000000007 eps = 10**-9 def main(): import sys input = sys.stdin.buffer.readline H, W, Q = map(int, input().split()) ans = H*W D = {} for _ in range(Q): h, w = map(int, input().split()) if w in D: hh = D[w] if h < hh: ans -= hh - h D[w] = h else: D[w] = h ans -= H - h + 1 print(ans) if __name__ == '__main__': main()