#yukicoder423E Warp Zone

H, W, N = map(int, input().split())
D = set([(1, 1), (H, W)])
I = [list(map(int, input().split())) for _ in range(N)]
for a, b, c, d in I:
    D.add((a, b))
    D.add((c, d))
D = sorted(D)
E = {(h, w): i for i, (h, w) in enumerate(D)}
G = [[] for _ in range(len(E))]
for a, b, c, d in I:
    G[ E[(a, b)] ].append( E[(c, d)] )

#distを計算
dist = lambda a, b, c, d: abs(a - c) + abs(b - d)
cost = [[0] * len(E) for _ in range(len(E))]
for i, (a, b) in enumerate(E):
    for j, (c, d) in enumerate(E):
        cost[i][j] = dist(a, b, c, d)

#原義dijkstra法
visited = [False] * len(E)
DP = [10 ** 18] * len(E)
DP[ E[(1, 1)] ] = 0
for _ in range(len(E)):
    x, y = 0, 10 ** 18
    for i in range(len(E)):
        if y > DP[i] and visited[i] == False:
            x, y = i, DP[i]
    i, ct = x, y
    DP[i] = 10 ** 18
    visited[i] = True
    if D[i] == (H, W):
        exit( print(ct) )
    for j in range(len(E)):
        if i == j: continue
        if visited[j] == True: continue
        DP[j] = min(DP[j], ct + cost[i][j])
    for j in G[i]:
        if i == j: continue
        if visited[j] == True: continue
        DP[j] = min(DP[j], ct + 1)