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

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)))
ans=W*H-other-N
print(ans)