#############################################################

import sys
sys.setrecursionlimit(10**7)

from heapq import heappop,heappush
from collections import deque,defaultdict,Counter
from bisect import bisect_left, bisect_right
from itertools import product,combinations,permutations

ipt = sys.stdin.readline

def iin():
    return int(ipt())
def lmin():
    return list(map(int,ipt().split()))

MOD = 998244353
#############################################################

H,W,N = lmin()
L = [lmin() for _ in range(N)]

d = defaultdict(int)
d[(1,1)] = 0
d[(H,W)] = 1
cnt = 2
S = [(1,1),(H,W)]
for a,b,c,D in L:
    d[(a,b)] = cnt
    S.append((a,b))
    cnt += 1
    d[(c,D)] = cnt
    S.append((c,D))
    cnt += 1


G = [[] for _ in range(cnt)]
for a,b,c,D in L:
    G[d[(a,b)]].append((d[(c,D)],1))

for i in range(cnt):
    i1,j1 = S[i]
    for j in range(cnt):
        if i==j:
            continue
        i2,j2 = S[j]
        G[i].append((j,abs(i1-i2)+abs(j1-j2)))

inf = 1<<60
hq = [(0,0)]
cost = [inf]*cnt
cost[0] = 0

while hq:
    cur,c1 = heappop(hq)
    for nxt,c2 in G[cur]:
        if c1+c2 >= cost[nxt]:
            continue
        cost[nxt] = c1+c2
        heappush(hq,(nxt,c1+c2))

print(cost[1])