import collections,sys,math,functools,operator,itertools,bisect,heapq,decimal,string,time,random
#sys.setrecursionlimit(10**9)
#sys.set_int_max_str_digits(0)
input = sys.stdin.readline
#n = int(input())
#alist = list(map(int,input().split()))
#alist = []
#s = input()
h,w,n = map(int,input().split())
v = 2*n+2
e = [[] for i in range(2*n+2)]
warp = []
warp.append((1,1))
for i in range(n):
    a,b,c,d = map(int,input().split())
    dist = abs(a-c) + abs(b-d)
    #e[2*i+2].append(2*i+1)
    e[2*i+1].append(2*i+2)
    warp.append((a,b))
    warp.append((c,d))
warp.append((h,w))

start = 0
d = []
dist = [10**18 for i in range(v)]
heapq.heappush(d,(0,start))
dist[start] = 0
while d:
    _,now = heapq.heappop(d)
    if _ > dist[now]:
        continue
    x,y = warp[now]
    for to in e[now]:
        if dist[to] > dist[now] + 1:
            dist[to] = dist[now] + 1
            heapq.heappush(d,(dist[to],to))
    for i in range(v):
        if i == now:
            continue
        tx,ty = warp[i]
        cost = abs(x-tx) + abs(y-ty)
        if dist[i] > dist[now] + cost:
            dist[i] = dist[now] + cost
            heapq.heappush(d,(dist[i],i))

print(dist[-1])