H,W,N = map(int,input().split())
ABCD = [list(map(int,input().split())) for _ in range(N)]
INF = H + W - 1
Start = []
E = [[] for _ in range(N+2)]

for i in range(N):
    a0,b0,c0,d0 = ABCD[i]
    E[0].append((i+1,a0+b0-2))
    for j in range(N):
        a1,b1,c1,d1 = ABCD[j]
        if i == j:
            continue
        E[i+1].append((j+1,abs(a1-c0) + abs(b1-d0)))
    E[i+1].append((N+1,abs(H-c0) + abs(W-d0)))

from heapq import *
D = [INF] * (N+2)

#普通のダイクストラ
def dijkstra():
    D[0] = 0
    q = [(0,0)]
    while len(q) > 0:
        d, u = heappop(q)
        #下のifでTLE解消することがある
        if d > D[u]: continue
        for a,b in E[u]:
            if D[a] > D[u] + b + 1:
                D[a] = D[u] + b + 1
                heappush(q, (D[a], a))
    return

dijkstra()
print(D[N+1] - 1)