from heapq import heappush, heappop def dijkstra(s, N): # (始点, ノード数) dist = [INF for _ in range(N)] hq = [(0, s)] dist[s] = 0 seen = [False] * N # ノードが確定済みかどうか while hq: d, v = heappop(hq) # ノードを pop する if seen[v]: continue seen[v] = True for to, cost in G[v]: # ノード v に隣接しているノードに対して if dist[v] + cost < dist[to]: dist[to] = dist[v] + cost heappush(hq, (dist[to], to)) return dist import sys input = sys.stdin.readline H, W, N = map(int, input().split()) ABCD = [list(map(int, input().split())) for _ in range(N)] G = [[] for _ in range(2*N+2)] INF = H+W st = 2*N ed = 2*N+1 G[st].append((ed, H-1+W-1)) G[ed].append((st, H-1+W-1)) for i in range(N): a, b, c, d = ABCD[i] u = i*2 v = i*2+1 G[u].append((v, 1)) G[v].append((u, abs(c-a)+abs(d-b))) G[st].append((u, a-1+b-1)) G[u].append((st, a-1+b-1)) G[ed].append((u, H-a+W-b)) G[u].append((ed, H-a+W-b)) G[st].append((v, c-1+d-1)) G[v].append((st, c-1+d-1)) G[ed].append((v, H-c+W-d)) G[v].append((ed, H-c+W-d)) for i in range(N): a, b, c, d = ABCD[i] u = i*2 v = i*2+1 for j in range(i+1, N): a2, b2, c2, d2 = ABCD[j] u2 = j*2 v2 = j*2+1 G[u].append((u2, abs(a2-a)+abs(b2-b))) G[u2].append((u, abs(a2-a)+abs(b2-b))) G[u].append((v2, abs(c2-a)+abs(d2-b))) G[v2].append((u, abs(c2-a)+abs(d2-b))) G[v].append((u2, abs(a2-c)+abs(b2-d))) G[u2].append((v, abs(a2-c)+abs(b2-d))) G[v].append((v2, abs(c2-c)+abs(d2-d))) G[v2].append((v, abs(c2-c)+abs(d2-d))) dist = dijkstra(st, 2*N+2) print(dist[ed])