import heapq

h,w,n=map(int,input().split())

wps=[]
wpt=[]
for i in range(n):
  a,b,c,d=map(int,input().split())
  wps.append([a,b])
  wpt.append([c,d])

def dist(x,y):
  return (abs(x[0]-y[0])+abs(x[1]-y[1]))

d=[10**18]*(2+n*2)
d[0]=0

g=[[] for _ in range(2+n*2)]
for i in range(n):
  g[0].append([2*i+2,dist([1,1],wps[i])])
  g[0].append([2*i+3,dist([1,1],wpt[i])])
g[0].append([1,dist([1,1],[h,w])])

for i in range(n):
  g[2*i+2].append([2*i+3,1])
  g[2*i+3].append([2*i+2,dist(wps[i],wpt[i])])
  g[2*i+2].append([1,dist(wps[i],[h,w])])
  g[2*i+3].append([1,dist(wpt[i],[h,w])])
  for j in range(n):
    if i==j:
      continue
    k=dist(wpt[i],wps[j])
    if 1+dist(wps[i],wps[j])<k:
      g[2*i+2].append([2*j+2,dist(wps[i],wps[j])])
    k=dist(wpt[i],wpt[j])
    if 1+dist(wps[i],wpt[j])<k:
      g[2*i+2].append([2*j+3,dist(wps[i],wpt[j])])
    g[2*i+3].append([2*j+2,dist(wpt[i],wps[j])])
    g[2*i+3].append([2*j+3,dist(wpt[i],wpt[j])])
    
hq=[(0,0)]

while hq:
  v,w=heapq.heappop(hq)
  if v>d[w]:
    continue
  if w==1:
    print(v)
    exit()
  for i,j in g[w]:
    if d[i]>v+j:
      d[i]=v+j
      heapq.heappush(hq,(v+j,i))