import heapq
from collections import defaultdict
H,W,N=map(int,input().split())
ABCD=[tuple(map(int,input().split())) for _ in range(N)]

dist=defaultdict(int)
pos=(1,1)
dist[pos]=0
Q=[]
heapq.heapify(Q)
heapq.heappush(Q,(dist[pos],pos))
while len(Q):
    e,(i,j)=heapq.heappop(Q)
    for (a,b,c,d) in ABCD:
        if (i,j)==(a,b):
            if dist.get((c,d)) is None or e+1<dist[(c,d)]:
                dist[(c,d)]=e+1
                heapq.heappush(Q,(dist[(c,d)],(c,d)))
        else:
            dd=abs(i-a)+abs(j-b)
            if dist.get((a,b)) is None or e+dd<dist[(a,b)]:
                dist[(a,b)]=e+dd
                heapq.heappush(Q,(dist[(a,b)],(a,b)))
    dd=abs(i-H)+abs(j-W)
    if dist.get((H,W)) is None or e+dd<dist[(H,W)]:
        dist[(H,W)]=e+dd
        heapq.heappush(Q,(dist[(H,W)],(H,W)))
print(dist[(H,W)])