#include <iostream>
using namespace std;
 
const int MAX_SIZE = 1000;
 
bool is_square(int upLeftX, int upLeftY, int k, short int mt[MAX_SIZE][MAX_SIZE]) {
	int sameDigit = mt[upLeftX][upLeftY];
	for (int s = 1; s <= k; ++s) {
		bool equals = mt[upLeftX][upLeftY + s] != sameDigit || mt[upLeftX + k][upLeftY + s] != sameDigit;
		if (equals || mt[upLeftX + s][upLeftY] != sameDigit || mt[upLeftX + s][upLeftY + k] != sameDigit) {
			return false;
		}
	}
	return true;
}
int biggestSquare(int sizeX, int sizeY, short int mt[MAX_SIZE][MAX_SIZE]) {
	int max = 1;
	for (int i = 1; i <= sizeX - max; ++i) {
		for (int j = 1; j <= sizeY - max; ++j) {
			for (int k = max; i + k <= sizeX && j + k <= sizeY; ++k) {
				if (is_square(i, j, k, mt)) {
					max = k + 1;
				}
			}
		}
	}
	return max;
}
 
int main() {
	int sizeX, sizeY;
	short int mt[MAX_SIZE][MAX_SIZE];
	cin >> sizeX >> sizeY;
	for (int i = 1; i <= sizeX; ++i) {
		for(int j = 1; j <= sizeY; ++j) {
			cin >> mt[i][j];
		}
	}
	cout << biggestSquare(sizeX, sizeY, mt);
	return 0;
}
 

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11 10
6	3	4	0	9	7	3	6	5	8
6	9	4	3	2	8	2	6	8	7
4	5	5	5	8	1	0	7	1	0
0	1	0	0	0	0	0	9	7	9
8	3	0	4	0	5	0	7	2	0
7	9	0	0	0	6	0	5	1	5
2	4	0	4	8	9	0	7	2	8
4	2	0	0	0	0	0	5	5	6
8	2	1	6	7	7	8	6	6	8
2	3	4	1	8	0	6	5	8	0
8	7	7	2	3	0	3	2	5	8