H,W,Q = map(int,input().split()) dic = {} ans = H*W for i in range(Q): y,x = map(int,input().split()) if x not in dic: dic[x] = y dame = H + 1 - y else: if y > dic[x]: dame = 0 else: dame = dic[x] - y dic[x] = min(dic[x],y) ans -= dame print(ans)