# 盤面が大きい、スタート、ゴール、ワープ地点間でダイクストラやるか

import sys
input = sys.stdin.readline

H, W, N = map(int, input().split())
dic = {}
edges = [[] for i in range(N*2+2)]
for i in range(N):
    a, b, c, d = map(int, input().split())
    dic[i*2] = (a, b)
    dic[i*2+1] = (c, d)
    edges[i*2].append((i*2+1, 1))
dic[N*2]=(1, 1)
dic[N*2+1]=(H, W)

for u in range(N*2+2):
    for v in range(N*2+2):
        if u == v:
            continue
        if 0<=u<N*2 and u%2 == 0 and v==u+1:
            continue
        
        d = abs(dic[u][0]-dic[v][0])+abs(dic[u][1]-dic[v][1])
        edges[u].append((v, d))
        #edges[v].append((u, d))

#print(edges)

from heapq import heappush, heappop
INF = 10 ** 18
def dijkstra(s, n, connect): #(始点, ノード数)
    distance = [INF] * n
    que = [(0, s)] #(distance, node)
    distance[s] = 0
    confirmed = [False] * n # ノードが確定済みかどうか
    while que:
        w,v = heappop(que)
        if distance[v]<w:
            continue
        confirmed[v] = True
        for to, cost in connect[v]: # ノード v に隣接しているノードに対して
            if confirmed[to] == False and distance[v] + cost < distance[to]:
                distance[to] = distance[v] + cost
                heappush(que, (distance[to], to))
    return distance

distance = dijkstra(N*2, N*2+2, edges)
ans = distance[N*2+1]
print(ans)