import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

W = int(readline())
H = int(readline())
N = int(readline())
m = map(int,read().split())
S,K = zip(*zip(m,m))

other = (W - len(set(S))) * (H - len(set(K)))
answer = W * H - other - N
print(answer)