#ifdef _WIN32
#  define LL "%I64d"
#else
#  define LL "%Ld"
#endif

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <ctime>
#include <vector>
#include <deque>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <bitset>
#include <string>
#include <algorithm>
#include <complex>
#include <utility>
#include <cassert>
using namespace std;
#define null NULL
#define mp make_pair
#define pb(a) push_back(a)
#define sz(a) ((int)(a).size())
#define all(a) a.begin() , a.end()
#define fi first
#define se second
#define relaxMin(a , b) (a) = min((a),(b))
#define relaxMax(a , b) (a) = max((a),(b))
#define SQR(a) ((a)*(a))
typedef vector<int> vi;
typedef pair<int,int> pii;
typedef long long ll;
const int MAXN = 1010;
char in[MAXN][MAXN];
int n, m;

bool Full(int j, char w){
  for(int i = 0;i < n - 1;++i){
    if(in[i][j] != w) return false;
  }
  return true;
}

void Say(string w){
  printf("%s\n", w.c_str());
  exit(0);
}

int main(){
  freopen("barcode.in", "r", stdin);
  freopen("barcode.out", "w", stdout);
  scanf("%d%d", &n, &m);
  for(int i = 0;i < n;++i)
   scanf("%s", in[i]);
  for(int j = 0;j < m;++j)
   if(in[n-1][j] < '1' || in[n-1][j] > '9')
    Say("NO");
  for(int j = 0;j < m;++j){
    if(!Full(j, '.') && !Full(j, '#'))
     Say("NO");
  }
  Say("BUY");
  return 0;
}