h, w, n = map(int, input().split())
C = [[1] * w for _ in range(h)]
for _ in range(n):
    a, b = map(int, input().split())
    C[a - 1][b - 1] = 0

for j in range(w):
    for i in range(1, h):
        if C[i][j] != 0:
            C[i][j] = C[i - 1][j] + 1

ans = 0
for row in C:
    tot = 0
    st = []
    for c in row:
        if c == 0:
            st = []
            tot = 0
            continue
        a = 1
        while st and st[-1][0] >= c:
            tot -= st[-1][0] * st[-1][1]
            a += st.pop()[1]
        st.append((c, a))
        tot += c * a

        ans += tot

print(ans)