W = int(input())
H = int(input())
N = int(input())
p = [[0]*H for i in range(W)]
for i in range(N):
        S, K = map(int,input().split())
        for j in range(W):      p[j][K-1]=1
        for j in range(H):      p[S-1][j]=1
n = sum([sum(x) for x in p])-N
print(n)