// {{{
#include <cstdio>
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <set>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <cassert>
#define SIZE(x) ((int) (x).size())
#define REP(i, n) for (int i = 0; i < (int) (n); ++i)
#define FOR(i, a, b) for (int i = (int) (a); i <= (int) (b); ++i)
#define FORD(i, a, b) for (int i = (int) (a); i >= (int) (b); --i)
#define FORE(i, c) for (__typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define DEBUG(x) { cerr << #x << ": " << (x) << endl; }
using namespace std;

typedef long long LL;
// }}}

#define MAXN 2007
#define SQR(x) ((x) * (x))

int A[3][MAXN][MAXN];
int D[MAXN][MAXN];

int horizontal(int x, int n, int m) {
	int res = 1;

	REP(i, n) REP(j, m) {
		if (i == 0 || j == 0) {
			D[i][j] = 1;
			continue;
		}
		D[i][j] = 1 + min(D[i - 1][j - 1], min(D[i - 1][j], D[i][j - 1]));
		if (D[i][j] < 4) {
			bool ok = true;
			FOR(ii, i - D[i][j] + 1, i) FOR(jj, j - D[i][j] + 2, j)
				if (A[x][ii][jj] != A[x][ii][jj - 1])
					ok = false;
			int d = A[x][i][j] - A[x][i - 1][j];
			FOR(ii, i - D[i][j] + 2, i)
				if (A[x][ii][j] - A[x][ii - 1][j] != d)
					ok = false;
			if (!ok)
				D[i][j] = 1;
		} else {
			if (A[x][i][j] != A[x][i][j - 1])
				D[i][j] = 1;
		}
		res = max(res, D[i][j]);
	}

	return SQR(res);
}

int diagonal(int x, int n, int m) {
	int res = 1;

	REP(i, n) REP(j, m) {
		if (i == 0 || j == 0) {
			D[i][j] = 1;
			continue;
		}
		D[i][j] = 1 + min(D[i - 1][j - 1], min(D[i - 1][j], D[i][j - 1]));
		if (D[i][j] < 3) {
			if (D[i][j] == 2) {
				if (A[x][i][j] != A[x][i - 1][j - 1] ||
				    A[x][i - 1][j] + A[x][i][j - 1] != 2 * A[x][i][j])
					D[i][j] = 1;
			}
		} else {
			if (A[x][i][j] != A[x][i - 1][j - 1])
				D[i][j] = 1;
		}
		res = max(res, D[i][j]);
	}

	return SQR(res);
}

int main() {
	int n, m;
	while (scanf("%d%d", &n, &m), n) {
		REP(i, n) REP(j, m) {
			scanf("%d", &A[0][i][j]);
			A[1][j][i] = A[0][i][j];
			A[2][i][m - j - 1] = A[0][i][j];
		}
		printf("%d\n", max(max(horizontal(0, n, m), horizontal(1, m, n)), max(diagonal(0, n, m), diagonal(2, n, m))));
	}
}