from heapq import*
(h,w),*a=[[*map(int,s.split())]for s in open(0)]
c=[[-1]*w for _ in range(h)]
c[0][0]=1
c[-1][-1]=0
q=[[]for _ in range(2)]
for i,j,k in[(1,0,1),(0,1,1),(w-2,h-1,0),(w-1,h-2,0)]:
  if 0<=i<h and 0<=j<w:
    q[k]+=(a[i][j],i,j),
q[0].sort()
q[1].sort()
k=1
while q[k]:
  p,i,j=heappop(q[k])
  if c[i][j]!=-1:
    continue
  c[i][j]=k
  ng=0
  for di,dj in[(-1,0),(1,0),(0,1),(0,-1)]:
    ni,nj=i+di,j+dj
    if 0<=ni<h and 0<=nj<w and c[ni][nj]==k^1:
      ng=1
  if ng:
    break
  for di,dj in[(-1,0),(1,0),(0,1),(0,-1)]:
    ni,nj=i+di,j+dj
    if 0<=ni<h and 0<=nj<w and c[ni][nj]==-1:
      heappush(q[k],(a[ni][nj],ni,nj))
  k^=1
print(sum(i!=-1for j in c for i in j)-2)