import sys
sys.setrecursionlimit(5*10**5)
input = sys.stdin.readline
from collections import defaultdict, deque, Counter
from heapq import heappop, heappush
from bisect import bisect_left, bisect_right
from math import gcd

h,w,n = map(int,input().split())
za = [list(map(int,input().split())) for i in range(n)]
graph = [[] for i in range(n+3)]
for i in range(n):
    ai,bi,ci,di = za[i]
    for j in range(n):
        if i == j: continue
        aj,bj,cj,dj = za[j]
        dis = abs(ci-aj) + abs(di-bj)
        graph[i].append((j, dis+1))
        graph[j].append((i, dis+1))
    graph[n].append((i, ai+bi-2))
    graph[i].append((n+1, abs(h-ci)+abs(w-di)))

#ダイクストラ法
def dijkstra(s,n): # sがスタート、nが頂点数
    INF = 10**15
    dist = [INF]*(n+1)
    que = [(0,s)]
    dist[s] = 0
    while que:
        c,crr = heappop(que)
        if c > dist[crr]: continue
        for nxt, cost in graph[crr]:
            if dist[crr] + cost < dist[nxt]:
                dist[nxt] = dist[crr] + cost
                heappush(que,(dist[nxt],nxt))
    return dist

d = dijkstra(n,n+2)

print(min(d[n+1]+1, h+w-2))