H,W,N=map(int,input().split())
result=H-1+W-1
from heapq import heappush,heappop
L=[]
for i in range(N):
  x,y,c,d=map(int,input().split())
  L.append((x,y,c,d))
kaku=[False]*N
dist=[10**15]*N
S=[]
for i in range(N):
  x,y=L[i][0],L[i][1]
  dist[i]=abs(x-1)+abs(y-1)
  heappush(S,dist[i]*10**10+i)
while S:
    w=heappop(S)
    time=w//(10**10)
    pos=w%(10**10)
    if kaku[pos]==True:
      continue
    kaku[pos]=True
    c,d=L[pos][2],L[pos][3]
    for j in range(N):
      if kaku[j]==True:
        continue
      x,y=L[j][0],L[j][1]
      di=abs(x-c)+abs(y-d)
      if dist[j]>dist[pos]+di+1:
        dist[j]=dist[pos]+di+1
        heappush(S,dist[j]*10**10+j)
for i in range(N):
    c,d=L[i][2],L[i][3]
    di=abs(c-H)+abs(d-W)
    result=min(result,dist[i]+di+1)
print(result)