#include <iostream>
#include <stdio.h>
#include <stdlib.h>

using namespace std;

int n, m;
char barcode[1001][1001];
bool buy = true;

void input()
{
    freopen("barcode.in", "r", stdin);
    scanf("%d%d", &n, &m);
    for (int i = 0; i < n; i++)
        scanf("%s", barcode[i]);
    fclose(stdin);
}

void calculate()
{
    if (n == 1)
    {
        buy = false;
        return;
    }
    for (int i = 0; i < m; i++)
        for (int j = 0; j < n - 1; j++)
        {
            if (((barcode[j][i] != '.') && (barcode[j][i] != '#')) || (barcode[0][i] != barcode[j][i]))
            {
                buy = false;
                return;
            }
        }
    for (int i = 0; i < m; i++)
        if ((barcode[n - 1][i] <= '0') || (barcode[n - 1][i] > '9'))
        {
            buy = false;
            return;
        }
}

void output()
{
    freopen("barcode.out", "w", stdout);
    if (buy) printf("BUY\n");
    else printf("NO\n");
    fclose(stdout);
}

int main()
{
    input();
    calculate();
    output();
	return 0;
}