#include <bits/stdc++.h>
#define endl '\n'
using namespace std;

const int maxN = 1005, maxM = 1005;

bool p = true;
int n, m;
char matrix[maxN][maxM];

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    freopen("barcode.in", "r", stdin);
    freopen("barcode.out", "w", stdout);

    cin>>n>>m;
    for(int i = 0; i < n; i++)
    {
        for(int j = 0; j < m; j++)
        {
            cin>>matrix[i][j];

            if(i != 0)
            {
                if(i != n - 1)
                {
                    if(matrix[i][j] == '#' && matrix[i - 1][j] != '#') p = false;
                }
                else
                {
                    if(matrix[i][j] > '9' || matrix[i][j] < '0') p = false;
                }
            }
        }
    }

    if(p) cout<<"BUY"<<endl;
    else cout<<"NO"<<endl;
    return 0;
}