from heapq import heappush, heappop
from collections import defaultdict

H, W, N = map(int, input().split())
warp = [list(map(int, input().split())) for _ in range(N)]
G = defaultdict(list)
G[(1, 1)].append((H, W, (H-1)+(W-1)))
for i in range(N):
    a, b, c, d = warp[i]
    G[(1, 1)].append((a, b, (a-1)+(b-1)))
    G[(a, b)].append((c, d, 1))
    G[(c, d)].append((H, W, (H-c)+(W-d)))
    for j in range(N):
        a2, b2, c2, d2 = warp[j]
        G[(c, d)].append((a2, b2, abs(a2-c)+abs(b2-d)))

def dijkstra(start):
    dist = defaultdict(int)
    dist[start] = 0
    visited = set()
    que = [(0, start)]
    while que:
        d, (h, w) = heappop(que)
        if (h, w) in visited:
            continue
        visited.add((h, w))
        for nh, nw, weight in G[(h, w)]:
            if (nh, nw) not in dist or dist[(h, w)]+weight < dist[(nh, nw)]:
                dist[(nh, nw)] = dist[(h, w)]+weight
                heappush(que, (dist[(nh, nw)], (nh, nw)))
    return dist

print(dijkstra((1, 1))[(H, W)])