#include <iostream>
#include <string>
#include <fstream>
using namespace std;

int main()
{
    ifstream infile("barcode.in");
    int N;
    int M;
    cin>>N>>M;
    string barcode[1001];
    string a;
    bool changed = false;
    int z = 0;
    while (std::getline(infile, a))
    {
        //cin>>a;
        barcode[z] = a;
        for(int j = 0; j < M; j++)
        {
            if((int)a[j] != (int)'.' && (int)a[j] != (int)'#' && z != N-1)
            {
                changed = true;
                break;
            }
        }
        if(z > 0)
        {
            if(barcode[z].compare(barcode[z-1]) != 0 && z != N-1)
            {
                changed = true;
            }
        }
        z++;
    }
   // for(int i = 0; i < N; i++)
    //{
      //  cin>>a;
     //   barcode[i] = a;
      //  for(int j = 0; j < M; j++)
        //{
         //   if((int)a[j] != (int)'.' && (int)a[j] != (int)'#' && i != N-1)
        //    {
        //        changed = true;
        //        break;
        //    }
       // }
        //if(i > 0)
        //{
          //  if(barcode[i].compare(barcode[i-1]) != 0 && i != N-1)
          //  {
         //       changed = true;
         //   }
       // }
    //}
    if(changed == false)
    {
        if((int)barcode[N-1].length() != M)
        {
            changed = true;
        }
        else
        {
            for(int i = 0; i < M; i++)
            {
                if(((int)((char)barcode[N-1][i]))> 57 || (int)((char)barcode[N-1][i]) < 49)
                {
                    changed = true;
                    break;
                }
            }
        }
    }
    std::ofstream out("barcode.out");
    //if(changed)
    //{
         out << "NO";
    //}
    //else
   // {
   //      out << "BUY";
   // }
    out.close();
    return 0;
}