from heapq import*
h,w,n=map(int,input().split())
dh={1,h}
dw={1,w}
ab=[[*map(int,input().split())]for i in range(n)]
for a,b,c,d in ab:dh|={a,c};dw|={b,d}
dh=sorted(dh)
dhd={j:i for i,j in enumerate(dh)}
dw=sorted(dw)
dwd={j:i for i,j in enumerate(dw)}
D=[[[-1,None]for j in range(len(dw))]+[[1,None]]for i in range(len(dh))]+[[[1,None]]*(len(dw)+1)]
for a,b,c,d in ab:D[dhd[a]][dwd[b]][1]=(dhd[c],dwd[d])
h=[(0,0,0)]
while h:
    e,a,b=heappop(h)
    if D[a][b][0]<0:
        D[a][b][0]=e
        if D[a][b][1]:
            c,d=D[a][b][1]
            if D[c][d][0]<0:heappush(h,(e+1,c,d))
        if D[a-1][b][0]<0:heappush(h,(e+dh[a]-dh[a-1],a-1,b))
        if D[a+1][b][0]<0:heappush(h,(e+dh[a+1]-dh[a],a+1,b))
        if D[a][b-1][0]<0:heappush(h,(e+dw[b]-dw[b-1],a,b-1))
        if D[a][b+1][0]<0:heappush(h,(e+dw[b+1]-dw[b],a,b+1))
print(D[-2][-2][0])