import heapq

H,W=map(int,input().split())
A=[list(map(int,input().split())) for h in range(H)]
color=[[None]*W for h in range(H)]
queue=[[(A[0][1],0,1),(A[1][0],1,0)],[(A[H-1][W-2],H-1,W-2),(A[H-2][W-1],H-2,W-1)]]
color[0][0]=0
color[H-1][W-1]=1
heapq.heapify(queue[0])
heapq.heapify(queue[1])
seen=[[[False]*W for h in range(H)] for c in range(2)]
seen[0][0][1]=1
seen[0][1][0]=1
seen[1][H-1][W-2]=1
seen[1][H-2][W-1]=1
ans=0
while True:
    c=ans%2
    a,h,w=heapq.heappop(queue[c])
    ans+=1
    color[h][w]=c
    skip=False
    for dh,dw in ((0,1),(1,0),(0,-1),(-1,0)):
        if 0<=h+dh<H and 0<=w+dw<W:
            if color[h+dh][w+dw]==None:
                if seen[c][h+dh][w+dw]:
                    continue
                heapq.heappush(queue[c],(A[h+dh][w+dw],h+dh,w+dw))
                seen[c][h+dh][w+dw]=True
            else:
                if color[h+dh][w+dw]!=c:
                    skip=True
    if skip:
        break
print(ans)