#include <fstream>
using namespace std;

int main()
{
	ifstream readfile("barcode.in");
	ofstream writefile("barcode.out");
	int size,n=0,m=0;
	bool isvalid = true;
	readfile >> n>> m;
	if (n < 1 || m < 1 || n>1000 || m>1000)
	{
		writefile << "NO";
		return 0;
	}
	size = n * m;
	char* barcode = new char[size];
	for (int i = 0; i < n * m; i++)
	{
		readfile >> barcode[i];
	}
	for (int i = 0; i < n*m-2*m; i ++ )
	{
		if (barcode[i] != barcode[i + m]||(barcode[i]!='.'&&barcode[i]!='#'))
		{
			isvalid = false;
		}
	}
	for (int i = m*(n - 1); i < m*n; i++)
	{
		if (barcode[i] != '1' && barcode[i] != '2' && barcode[i] != '3' && barcode[i] != '4' && barcode[i] != '5' && barcode[i] != '6' && barcode[i] != '7' && barcode[i] != '8' && barcode[i] != '9')
		{
			isvalid = false;
		}
	}
	if (isvalid == true)
	{
		writefile << "BUY";
	}
	else
	{
		writefile << "NO";
	}

	return 0;
}