W = int(input())
H = int(input())
N = int(input())
cnt = [0]*W
s = set()

for _ in range(N):
    Si, Ki = map(int, input().split())
    Si -= 1
    cnt[Si] += 1
    s.add(Ki)
    
ans = 0

for c in cnt:
    if c==0:
        ans += len(s)
    else:
        ans += H-c

print(ans)