import sys, math sys.setrecursionlimit(10**8) sys.set_int_max_str_digits(0) INF = 1e18 MOD = 998244353 from bisect import bisect_left, bisect_right from collections import deque, defaultdict, Counter from itertools import product, combinations, permutations, groupby, accumulate from heapq import heapify, heappop, heappush from sortedcontainers import SortedList input = sys.stdin.readline def I(): return input().rstrip() def II(): return int(input().rstrip()) def IS(): return input().rstrip().split() def MII(): return map(int, input().rstrip().split()) def LI(): return list(input().rstrip()) def TII(): return tuple(map(int, input().rstrip().split())) def LII(): return list(map(int, input().rstrip().split())) def LSI(): return list(map(str, input().rstrip().split())) def GMI(): return list(map(lambda x: int(x) - 1, input().rstrip().split())) def kiriage(a, b): return (a+b-1)//b H, W, Q = MII() nokori = H*W memo = defaultdict(lambda: H + 1) for i in range(Q): y, x = MII() cur = memo[x] if y < cur: # 小さくできるならする diff = cur - y nokori -= diff memo[x] = y print(nokori)