import heapq

def f(s, n, edge):
    dist = [float("Inf")]*n
    dist[s] = 0
    hq = [[0,s]]
    heapq.heapify(hq)
    while len(hq) > 0:
        d,i = heapq.heappop(hq)
        if dist[i] < d:
            continue
        for j,d_1 in edge[i]:
            if dist[j] > (dist[i] + d_1):
                dist[j] = dist[i] + d_1
                heapq.heappush(hq, [dist[j],j])
    return dist


H,W,N = map(int,input().split())
s = 0
g = 2*N + 1
G = [[] for i in range(2*N+2)]
G[s].append((g,H+W-2))
for i in range(1,N+1):
  a,b,c,d = map(int,input().split())
  u,v = i,i+N
  G[0].append((u,a+b-2))
  G[u].append((v,1))
  G[v].append((g,H+W-c-d))

dist = f(0,2*N+2,G)
print(dist[g])