#include <fstream>
#include <cstring>


int main()
{
	std::ifstream inputFile;
	inputFile.open("barcode.in");

	short int rows;
	short int columns;

	inputFile >> rows;

	inputFile >> columns;

	int* activeRow = new int[columns];

	std::memset(activeRow, 0, (sizeof(activeRow)*columns));

	char myChar;

	bool fail = 0;

	for (int i = 0; i < columns; i++)
	{
		inputFile >> myChar;
		if (myChar == '#' || myChar == '.')
		{
			activeRow[i] = myChar;
		}
		else
		{
			fail = 1;
			break;
		}
	}

	if (fail == 0)
	{
		for (int row = 1; row < rows; row++)
		{
			for (int i = 0; i < columns; i++)
			{
				inputFile >> myChar;
				if ((activeRow[i] != 0) && (activeRow[i] != myChar))
				{
					fail = 1;
					break;
				}
			}
		}
	}

	int myInt;

	if (fail == 0)
	{
		for (int i = 0; i < columns; i++)
		{
			inputFile >> myInt;
			if ((myInt < 0)||(myInt > 9))
			{
				fail = 1;
				break;
			}
		}
	}

	std::ofstream outputFile;
	outputFile.open("barcode.out");

	if (fail == 0)
	{
		outputFile << "BUY";
	}
	else
	{
		outputFile << "NO";
	}
	return 0;
}