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

#define rep(i,x,y) for(int i=x;i<y;i++)
#define repr(i,x,y) for(int i=x;i>=y;i--)
#define int long long
#define pb push_back
#define ff first
#define ss second
#define sz(x) ((int)x.size())
#define all(x) begin(x), end(x)
#define memo(x,y) memset((x),(y),sizeof((x)))
#define line cout<<"[At "<<__LINE__<<"]"<<endl;

using pii = pair<int, int>;
using vi = vector<int>;
using vii = vector<pair<int, int>>;

constexpr int mod = 1e9 + 7, N = 2e5 + 5;
constexpr long long inf = 1e18;
constexpr long double eps = 1e-6;


void Onigiri() {
  int n, m;
  cin >> n >> m;
  int a[n][m];
  rep(i, 0, n)
    rep(j, 0, m)
      cin >> a[i][j];

  int dpl[n][m], dpu[n][m], dp[n][m];
  rep(i, 0, n) {
    rep(j, 0, m) {
      dpl[i][j] = 1;
      if(j != 0 && a[i][j - 1] == a[i][j])
        dpl[i][j] += dpl[i][j - 1];
    }
  }
  rep(i, 0, m) {
    rep(j, 0, n) {
      dpu[j][i] = 1;
      if(j != 0 && a[j - 1][i] == a[j][i])
        dpu[j][i] += dpu[j - 1][i];
    }
  }
  int ans = 0;
  rep(i, 0, n) {
    rep(j, 0, m) {
      dp[i][j] = 1;
      if(i > 0 && j > 0) {
        if(a[i - 1][j - 1] == a[i][j]) {
          int l = dpl[i][j];
          int u = dpu[i][j];
          dp[i][j] = min({dp[i - 1][j - 1] + 1, l, u});
        }
      }
      ans = max(ans, dp[i][j]);
    }
  }
  cout << ans;
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
#ifdef Zoro
  freopen("/home/pritish/Competitive/in", "r", stdin);
  freopen("/home/pritish/Competitive/out", "w", stdout);
#endif

  int t = 1;
  // cin>>t;

  while(t--) {
    Onigiri();
    cout << "\n";
  }

  cerr << "\n" << (float)clock() / CLOCKS_PER_SEC * 1000 << " ms" << endl;
  return 0;
}