h,w,n=map(int,input().split())
o=[tuple(map(int,input().split())) for i in range(n)]
e=[[] for i in range(n+2)]
for i in range(n):
	a,b,c,d=o[i]
	e[n]+=[(i,abs(a-1)+abs(b-1))]
	e[i]+=[(n+1,abs(h-c)+abs(w-d))]
	for j in range(n):
		if i!=j:
			a2,b2,c2,d2=o[j]
			e[i]+=[(j,abs(c-a2)+abs(d-b2))]
v=[h+w-2]*(n+2)
v[n]=0
q=[]
from heapq import heappush,heappop
heappush(q,(0,n))
while len(q)>0:
	sc,sp=heappop(q)
	if sc>v[sp]:
		continue
	for tp,tc in e[sp]:
		if v[tp]>sc+tc:
			v[tp]=sc+tc
			heappush(q,(v[tp],tp))
print(v[n+1])