#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)

struct Grid {
  int h;
  int w;
  Grid (int h, int w) : h(h), w(w) {}
};

struct Walk {
  int val;
  int length;
  Walk (int val, int length) : val(val), length(length) {}
};

int main() {
  int H, W;
  cin >> H >> W;
  map<int, vector<Grid>> g;
  rep(h, H) rep(w, W) {
    int val;
    cin >> val;
    g[val].push_back(Grid(h, w));
  }
  vector<int> dh = {0, 1, 0, -1};
  vector<int> dw = {1, 0, -1, 0};
  vector<vector<Walk>> dp(H, vector<Walk> (W, Walk(0, 0)));
  int length = 1;
  for (auto it = g.begin(); it != g.end(); it++) {
    int val = it->first;
    for (Grid p : it->second) {
      int len = -1;
      rep(i, 4) {
	int nh = p.h + dh[i];
	int nw = p.w + dw[i];
	if (nh < 0 || nh > H-1 || nw < 0 || nw > W-1) continue;
	if (dp[nh][nw].val < val)
	  len = max(dp[nh][nw].length, len);
      }
      if (len >= 0) {
	dp[p.h][p.w] = {val, len + 1};
	length = max(len + 1, length);
      }
    }
  }
  cout << length << endl;
  return 0;
}