#yukicoder423E Warp Zone

#入力受取  点は座標圧縮する
H, W, N = map(int, input().split())
P = set([(1, 1), (H, W)])
X = [tuple(map(int, input().split())) for _ in range(N)]
for a, b, c, d in X:
    P.add((a, b))
    P.add((c, d))
P = sorted(P)
R = {(x, y): i for i, (x, y) in enumerate(P)}
M = len(P)

#二点間距離をdistに格納  これ以降、座標を陽に持つ必要がなくなる
dist = lambda P1, P2: abs(P1[0] - P2[0]) + abs(P1[1] - P2[1])
D = [[dist(P1, P2) for P2 in P] for P1 in P]
del P

#ワープを反映
G = [[] for _ in range(M)]
for a, b, c, d in X:
    G[ R[(a, b)] ].append( R[(c, d)] )
S, E = R[(1, 1)], R[(H, W)]
del R

#オリジナルダイクストラ法
DP = [10 ** 18] * M
checked = [False] * M
DP[S] = 0

for _ in range(M):
    d, i = min([(DP[i], i) for i in range(M) if checked[i] == False])
    checked[i] = True
    for j in range(M):
        if checked[j]:
            assert DP[j] <= DP[i] + D[i][j]
        DP[j] = min(DP[j], DP[i] + D[i][j])
    for j in G[i]:
        if checked[j]:
            assert DP[j] <= DP[i] + 1
        DP[j] = min(DP[j], DP[i] + 1)

#答えを出力
print(DP[E])