from heapq import heapify, heappop, heappush
H, W, N = map(int, input().split())
G = [[] for _ in range(2 * N + 2)]
G[0].append((2 * N + 1, H - 1 + W - 1))
for i in range(1, 2 * N + 1, 2):
    a, b, c, d = map(int, input().split())
    a -= 1; b -= 1; c -= 1; d -= 1
    G[0].append((i, a + b))
    G[i].append((i + 1, 1))
    G[i + 1].append((2 * N + 1, H - 1 - c + W - 1 - d))
dist = [10 ** 18] * (2 * N + 2)
dist[0] = 0
pq = [(0, 0)]
heapify(pq)
while len(pq) > 0:
    d, u = heappop(pq)
    for v, c in G[u]:
        if dist[v] > dist[u] + c:
            dist[v] = dist[u] + c
            heappush(pq, (dist[v], v))
print(dist[2 *N + 1])