import sys
input = sys.stdin.readline

inf = 10 ** 18
def dijkstra(G, ind, N):
    seen = [0] * N
    dist = [inf] * N
    dist[ind] = 0
    while True:
        minv = inf
        for i in range(N):
            if seen[i]:
                continue
            if dist[i] < minv:
                ind = i
                minv = dist[i]
        if ind == N - 1:
            break
        seen[ind] = True
        for u in range(N):
            if seen[u]:
                continue
            dist[u] = min(dist[u], dist[ind] + G[ind][u])
    return dist[-1]


H, W, N = map(int, input().split())
M = 2 * N + 2
G = [[0] * M for _ in range(M)]
D = [(1, 1)]
for i in range(N):
    a, b, c, d = map(int, input().split())
    D.append((a, b))
    D.append((c, d))
    
D.append((H, W))
for i in range(M):
    for j in range(M):
        G[i][j] = abs(D[i][0] - D[j][0]) + abs(D[i][1] - D[j][1])
        
for i in range(N):
    G[2 * i + 1][2 * i + 2] = 1
    
print(dijkstra(G, 0, M))