#include <iostream>
#include <fstream>

using namespace std;

//#define DEBUG_OUTPUT

const char* INPUT_FILE_NAME = "barcode.in";
const char* OUTPUT_FILE_NAME = "barcode.out";

const int MAX_BARCODE_SIZE = 1000;

int barcodeHeight, barcodeWidth;
char barcode[MAX_BARCODE_SIZE][MAX_BARCODE_SIZE];

void readInput()
{
  ifstream finp(INPUT_FILE_NAME);
  finp >> barcodeHeight >> barcodeWidth;
  for (int x = 0; x < barcodeHeight; ++x)
    for (int y = 0; y < barcodeWidth; ++y)
      finp >> barcode[x][y];
#ifdef DEBUG_OUTPUT
  cout << barcodeHeight << " " << barcodeWidth << endl;
  for (int x = 0; x < barcodeHeight; ++x)
  {
    for (int y = 0; y < barcodeWidth; ++y)
      cout << barcode[x][y];
    cout << endl;
  }
#endif
}

bool isValid()
{
  for (int y = 0; y < barcodeWidth; ++y)
  {
    char first = barcode[0][y];
    int x;
    for (x = 0; x < barcodeHeight - 1; ++x)
    {
      if (barcode[x][y] != '.' && barcode[x][y] != '#')
        return false;
      if (barcode[x][y] != first)
        return false;
    }
    if (barcode[x][y] < '1' || barcode[x][y] > '9')
      return false;
  }
  return true;
}

void writeOutput(bool isValid)
{
  ofstream fout(OUTPUT_FILE_NAME);
  fout << (isValid ? "BUY" : "NO") << endl;
#ifdef DEBUG_OUTPUT
  cout << (isValid ? "BUY" : "NO") << endl;
#endif
}

int main()
{
  readInput();
  bool valid = isValid();
  writeOutput(valid);

  return 0;
}