from collections import deque

H, W, N = map(int, input().split())
A = []
B = []
for i in range(N):
    a, b = map(int, input().split())
    A.append(a - 1)
    B.append(b - 1)
c = [[0 for _ in range(W)] for _ in range(H)]
for i in range(N):
    c[A[i]][B[i]] = 1
length = [[0 for _ in range(W)] for _ in range(H)]
for j in range(W):
    if c[H - 1][j] == 0:
        length[H - 1][j] = 1
    else:
        length[H - 1][j] = 0
for i in reversed(range(H - 1)):
    for j in range(W):
        if c[i][j] == 0:
            length[i][j] = length[i + 1][j] + 1
        else:
            length[i][j] = 0

# print(length)
ans = 0
dq = deque()

dq.append([-1, -1])
now = 0

for i in range(H):
    for j in range(W):
        idx = j
        while True:
            if len(dq) == 0:
                break
            height, width = dq.pop()
            if height < length[i][j]:
                dq.append([height, width])
                break
            now -= height * width
            idx -= width
        now += length[i][j] * (j - idx + 1)
        ans += now
        dq.append([length[i][j], j - idx + 1])
    while len(dq):
        dq.pop()
    now = 0
print(ans)