H,W=map(int,input().split())
A=[list(map(int,input().split())) for _ in range(H)]

indegs=[[0 for _ in range(W)] for _ in range(H)]
for i in range(H):
    for j in range(W):
        for (di,dj) in [(1,0),(-1,0),(0,1),(0,-1)]:
            ni=i+di
            nj=j+dj
            if ni not in range(H) or nj not in range(W):continue
            if A[i][j]>A[ni][nj]:indegs[i][j]+=1

Q=[]
INF=int(1e18)
dist=[[0 for _ in range(W)] for _ in range(H)]
for i in range(H):
    for j in range(W):
        if indegs[i][j]==0:
            Q.append((i,j))
            dist[i][j]=1

while len(Q):
    i,j=Q.pop()
    for (di,dj) in [(1,0),(-1,0),(0,1),(0,-1)]:
        ni=i+di
        nj=j+dj
        if ni not in range(H) or nj not in range(W):continue
        if A[i][j]>=A[ni][nj]:continue
        indegs[ni][nj]-=1
        dist[ni][nj]=max(dist[ni][nj],dist[i][j]+1)
        if indegs[ni][nj]==0:Q.append((ni,nj))

ans=0
for i in range(H):
    for j in range(W):
        ans=max(ans,dist[i][j])
print(ans)