import sys
from collections import namedtuple

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

INF = 10**10

Segment = namedtuple('Segment', ('x', 'y', 'dx', 'dy', 'n'))
Rectangle = namedtuple('Rectangle', ('x1', 'y1', 'x2', 'y2'))
Pt = namedtuple('Pt', ('x', 'y'))

W, H = map(int, readline().split())
N = int(readline())
m = map(int, read().split())
XY = zip(m, m)
x0, y0 = next(XY)

def solve_two(x0, y0, x, y):
    if x0 > x:
        x0, x = x, x0
        y0, y = y, y0
    dx = x - x0
    dy = y - y0
    if (dx + dy) % 2 != 0:
        return
    if dx == abs(dy):
        if dy > 0:
            yield Rectangle(-INF, y, x0, INF)
            yield Rectangle(x, -INF, INF, y0)
            if dx > 1:
                yield Segment(x0 + 1, y - 1, 1, -1, dx - 2)
        else:
            yield Rectangle(-INF, -INF, x0, y)
            yield Rectangle(x, y0, INF, INF)
            if dx > 1:
                yield Segment(x0 + 1, y + 1, 1, 1, dx - 2)
        return
    d = (dx + abs(dy)) // 2
    if dx == 0:
        y = (y + y0) // 2
        yield Segment(-INF, y, 1, 0, INF * 2)
    elif dy == 0:
        x = (x + x0) // 2
        yield Segment(x, -INF, 0, 1, INF * 2)
    elif dx < dy:
        yield Segment(x0,y0+d,-1,0,INF)
        yield Segment(x, y-d, 1, 0, INF)
        if dx > 1:
            yield Segment(x0+1,y0-1,1,-1,dx-2)
    elif 0 < dy < dx:
        yield Segment(x-d,y,0,1,INF)
        if dy > 1:
            yield Segment(x - d + 1, y - 1, 1, -1, dy - 2)
        yield Segment(x0 + d, y0, 0, -1, INF)
    elif 0 < dx < -dy:
        yield Segment(x0, y0-d, -1, 0, INF)
        if dx > 1:
            yield Segment(x0+1,y0-d+1,1,1,dx - 2)
        yield Segment(x, y + d, 1, 0, INF)
    elif 0 < -dy < dx:
        yield Segment(x0+d,y0, 0, 1, INF)
        if -dy > 1:
            yield Segment(x-d+1,y+1, 1, 1, -dy - 2)
        yield Segment(x-d,y,0,-1,INF)
    else:
        raise Exception

def modify(seg):
    x,y,dx,dy,n = seg
    if dx == -1:
        return Segment(x+dx*n,y+dy*n,-dx,-dy,n)
    if dx == 0 and dy == -1:
        return Segment(x,y-n,0,1,n)
    return seg

def ptpt(pt1, pt2):
    if pt1.x == pt2.x and pt1.y == pt2.y:
        return pt1
    else:
        return None

def segpt(seg, pt):
    seg = modify(seg)
    d = abs(seg.x - pt.x) + abs(seg.y - pt.y)
    k = d // (abs(seg.dx) + abs(seg.dy))
    if not (0 <= k <= seg.n):
        return None
    if seg.x + seg.dx * k == pt.x and seg.y + seg.dy * k == pt.y:
        return pt
    return None

def recpt(rec, pt):
    if (rec.x1 <= pt.x <= rec.x2) and (rec.y1 <= pt.y <= rec.y2):
        return pt
    return None

def recrec(rec1, rec2):
    x1 = max(rec1.x1, rec2.x1)
    x2 = min(rec1.x2, rec2.x2)
    y1 = max(rec1.y1, rec2.y1)
    y2 = min(rec1.y2, rec2.y2)
    if x1 <= x2 and y1 <= y2:
        return Rectangle(x1, y1, x2, y2)
    return None

def recseg(rec, seg):
    seg = modify(seg)
    if seg.dx == 0:
        if not (rec.x1 <= seg.x <= rec.x2):
            return None
        low_x, high_x = 0, INF * 2
    elif seg.dx == 1:
        low_x, high_x = rec.x1 - seg.x, rec.x2 - seg.x
    else:
        low_x, high_x = x - rec.x2, x - rec.x1
    if seg.dy == 0:
        if not (rec.y1 <= seg.y <= rec.y2):
            return None
        low_y, high_y = 0, INF * 2
    elif seg.dy == 1:
        low_y, high_y = rec.y1 - seg.y, rec.y2 - seg.y
    else:
        low_y, high_y = y - rec.y2, y - rec.y1
    low = max(low_x, low_y, 0)
    high = min(high_x, high_y, seg.n)
    if low > high:
        return None
    return Segment(seg.x + seg.dx * low, seg.y + seg.dy * low, seg.dx, seg.dy,
                   high - low)

def segseg(seg1, seg2):
    seg1 = modify(seg1)
    seg2 = modify(seg2)
    x1, y1, a1, b1 = seg1.x, seg1.y, seg1.dx, seg1.dy
    x2, y2, a2, b2 = seg2.x, seg2.y, seg2.dx, seg2.dy
    det = -a1 * b2 + a2 * b1
    if det != 0:
        x, y = x2 - x1, y2 - y1
        s = (-b2 * x + a2 * y) // det
        t = (-b1 * x + a1 * y) // det
        if not ((0 <= s <= seg1.n) and (0 <= t <= seg2.n)):
            return None
        x, y = x1 + a1 * s, y1 + b1 * s
        if (x != x2 + a2 * t) or (y != y2 + b2 * t):
            return None
        return Pt(x, y)
    x1, y1, a1, b1 = seg1.x, seg1.y, seg1.dx, seg1.dy
    x2, y2, a2, b2 = seg2.x, seg2.y, seg2.dx, seg2.dy
    assert a1 == a2 and b1 == b2
    a, b = a1, b1
    if b * x1 - a * y1 != b * x2 - a * y2:
        # 交わらない平行線
        return None
    # 直線として同じ
    if a == 1:
        low_x = max(x1, x2)
        high_x = min(x1 + seg1.n, x2 + seg2.n)
        if low_x > high_x:
            return None
        return Segment(low_x, y1 + b * (low_x - x1), a, b, high_x - low_x)
    assert a == 0 and b == 1
    low_y = max(y1, y2)
    high_y = min(y1 + seg1.n, y2 + seg2.n)
    if low_y > high_y:
        return None
    return Segment(x1, low_y, 0, 1, high_y - low_y)

def intersect_two(shape1, shape2):
    if isinstance(shape1, Rectangle):
        if isinstance(shape2, Rectangle):
            return recrec(shape1, shape2)
        if isinstance(shape2, Segment):
            return recseg(shape1, shape2)
        return recpt(shape1, shape2)
    if isinstance(shape1, Segment):
        if isinstance(shape2, Rectangle):
            return recseg(shape2, shape1)
        if isinstance(shape2, Segment):
            return segseg(shape1, shape2)
        return segpt(shape1, shape2)
    if isinstance(shape2, Rectangle):
        return recpt(shape2, shape1)
    if isinstance(shape2, Segment):
        return segpt(shape2, shape1)
    return ptpt(shape1, shape2)

def intersect(pts1, pts2):
    for shape1 in pts1:
        for shape2 in pts2:
            shape = intersect_two(shape1, shape2)
            if shape is None:
                continue
            yield shape

def count_pt(shape):
    if isinstance(shape, Rectangle):
        return (shape.x2 - shape.x1 + 1) * (shape.y2 - shape.y1 + 1)
    if isinstance(shape, Segment):
        return shape.n + 1
    return 1

pts = [Rectangle(1, 1, W, H)]
for x, y in zip(m, m):
    pts1 = list(solve_two(x0, y0, x, y))
    pts = list(intersect(pts, pts1))

answer = 0
for shape in pts:
    answer += count_pt(shape)

print(answer)