H, W, N = map(int, input().split())

abcds = [tuple(map(int, input().split())) for _ in range(N)]

vs = [(1, 1)] + [(a, b) for a, b, c, d in abcds] + [(c, d) for a, b, c, d in abcds] + [(H, W)]

dist = [(1 << 60)] * len(vs)

dist[0] = 0
done = [False] * len(vs)

while True:
    # Dijkstra
    v = -1
    for i in range(len(vs)):
        if not done[i] and (v == -1 or dist[i] < dist[v]):
            v = i

    if v == -1:
        break

    done[v] = True

    x0, y0 = vs[v]
    d0 = dist[v]

    for i, (x1, y1) in enumerate(vs):
        if done[i]:
            continue

        d = abs(x1 - x0) + abs(y1 - y0)

        if d0 + d < dist[i]:
            dist[i] = d0 + d

    for i in range(N):
        dist[N + i + 1] = min(dist[N + i + 1], dist[i + 1] + 1)

print(dist[-1])