import sys
input = sys.stdin.readline

from operator import itemgetter
from heapq import heappop,heappush

H,W,N=map(int,input().split())
WA=[list(map(int,input().split())) for i in range(N)]

WA=[[1,1,1,1]]+WA+[[H,W,H,W]]

DP=[1<<63]*len(WA)
WA.sort(key=itemgetter(0))
WA.sort(key=itemgetter(1))

DP[0]=0

Q=[(0,0)]

while Q:
    time,ind=heappop(Q)

    if DP[ind]!=time:
        continue

    a,b,c,d=WA[ind]
    for j in range(len(WA)):
        e,f,g,h=WA[j]

        if a<=e and b<=f:
            dis=(e-a)+(f-b)

            if DP[j]>DP[ind]+dis:
                DP[j]=DP[ind]+dis
                heappush(Q,(DP[j],j))

        if c<=e and d<=f:
            dis=(e-c)+(f-d)

            if DP[j]>DP[ind]+dis+1:
                DP[j]=DP[ind]+dis+1
                heappush(Q,(DP[j],j))


print(DP[-1])