from collections import deque

H, W = map(int, input().split())

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

indeg = [0] * (H * W)
dh = [0, 1, 0, -1]
dw = [1, 0, -1, 0]

for h in range(H):
    for w in range(W):
        for k in range(4):
            nh = h + dh[k]
            nw = w + dw[k]

            if nh < 0 or nh >= H or nw < 0 or nw >= W : continue
            if A[h][w] < A[nh][nw]:
                indeg[nh * W + nw] += 1

dp = [0] * (H * W)
nxt = deque()
for i in range(H * W):
    if indeg[i] == 0 : nxt.append(i)

while nxt:
    pos = nxt.popleft()
    h = pos // W
    w = pos % W
    for k in range(4):
        nh = h + dh[k]
        nw = w + dw[k]
        if nh < 0 or nh >= H or nw < 0 or nw >= W : continue
        if A[h][w] < A[nh][nw]:
            t = nh * W + nw
            indeg[t] -= 1
            if indeg[pos] == 0 : nxt.append((t))
            dp[t] = max(dp[t], dp[pos] + 1)

print(max(dp) + 1)