h,w,n = map(int,input().split())
s = set()
abcd = [tuple(map(int,input().split())) for _ in range(n)]
for a,b,c,d in abcd: s |= {(a,b),(c,d)}
s = [(1,1)]+list(s)+[(h,w)]; m = len(s)
p = {v:i for i,v in enumerate(s)}
q = [[10**18]*m for _ in range(m)]
for a,b,c,d in abcd: q[p[(a,b)]][p[(c,d)]] = 1
for i in range(m):
    a,b = s[i]
    for j in range(m):
        c,d = s[j]
        q[i][j] = min(q[i][j],abs(a-c)+abs(b-d))
x = [0]+[10**18]*(m-1); f = [True]*m
for _ in range(m):
    z = 10**18; u = -1
    for i in range(m):
        if f[i] and x[i]<z: z = x[i]; u = i
    f[u] = False
    for v in range(m): x[v] = min(x[v],z+q[u][v])
print(x[-1])