from collections import deque

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

to = [set() for _ in range(H*W)]
for x in range(H*W):
    i, j = divmod(x, W)
    for di, dj in ((1, 0), (0, 1), (-1, 0), (0, -1)):
        ni, nj = i+di, j+dj
        if 0 <= ni < H and 0 <= nj < W and A[ni][nj] > A[i][j]:
            to[x].add(ni*W+nj)

indegree = [0]*(H*W)
for x in range(H*W):
    for y in to[x]:
        indegree[y] += 1

B = [x for x in range(H*W) if indegree[x] == 0]
q = deque(B)
order = []
while q:
    x = q.popleft()
    order.append(x)
    for y in to[x]:
        indegree[y] -= 1
        if indegree[y] == 0:
            q.append(y)

ans = 0
for x in B:
    # xからスタート
    i = order.index(x)
    dist = [-1]*(H*W)
    dist[x] = 1
    while i < len(order):
        x = order[i]
        i += 1
        for y in to[x]:
            dist[y] = max(dist[y], dist[x]+1)
    ans = max(ans, max(dist))

print(ans)