#include <cstdio>
#include <cmath>
#include <cstring>
#include <cctype>
#include <cstdlib>
#include <climits>
#include <vector>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <list>
#include <algorithm>
#include <string>

using namespace std;

#define FOR(i,m,n) for (int i = m; i < n; i++)



int values[2020][2020];
int square[2020][2020];
int typ[2020][2020];

int main() {
  
  while(1){
    int H, W;
    scanf("%d%d",&H,&W);
    if (H==0 && W==0) break;
    for(int h=0;h<H;++h){
      for(int w=0;w<W;++w){
        scanf("%d", &values[h][w]);
        square[h][w] = 1;
        typ[h][w] = -1;
      }
    }
    int ret = 0;
    FOR (h, 1, H) {
      FOR (w, 1, W) {
        int dx0 = values[h][w-1] - values[h][w];
        int dy0 = values[h-1][w] - values[h][w];
        int dx1 = values[h-1][w-1] - values[h-1][w];
        int dy1 = values[h-1][w-1] - values[h][w-1];
        int velikost = min(min(square[h-1][w-1], square[h][w-1]), square[h-1][w]);
        bool zmeneno = false;
        // diag
        if (dx1==dx0 && dy1==dy0&& abs(dx0)==abs(dy0)) {
          typ[h][w] = 3;
          zmeneno = true;
        }
        else if (dy1==0 && dy0==0 && dx0==dx1) {
          typ[h][w] = 2;
          zmeneno = true;
        }
        else if (dx1==0 && dx0==0 && dy0==dy1) {
          typ[h][w] = 1;
          zmeneno = true;
        }
        if (typ[h][w]!=-1) {
          square[h][w] = velikost + 1;
        }
        if (square[h][w] > 2) {
          int dx2 = values[h][w-2] - values[h][w-1];
          int dy2 = values[h-2][w] - values[h-1][w];
          if (dx2!=dx0 || dy2!=dy0)
            square[h][w] = 2;
        }
        ret = max(ret, square[h][w]);
      }
    }
    printf("%d\n", ret*ret);
  }
  return 0;
}