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import java.util.Scanner;
class main
{

   public static void main(String[] args)
   {
           Scanner in = new Scanner(System.in);
           int n = in.nextInt();
           int k = in.nextInt();
          
           litera[] slowo = new litera[n];           
           for(int i = 0; i< slowo.length; i++)
           {
               slowo[i] = new litera();
           }
          
           int poz = 0;
           boolean b;
           boolean exit = false;
          
           for(int i = 0; i< k;i++) //krok
           {
               do{
                   if(poz == 0)
                   {
                       b = false;
                       if(slowo[poz].next())
                       {
                           exit = true;
                       }
                   }
                   else
                   {
                       b = slowo[poz].next(slowo[poz - 1].value);
                   }

                   if(b)
                   {
                       poz--;


                   }
                   else
                   {
                       if(poz < n - 1)
                       {
                           poz++;
                       }
                   }
               }
               while (b);
              
             

               if(exit) break;
           }   
           if(exit)
           {
               System.out.println("NIE");
           }
           else
           {
               for(int j= 0; j<n;j++)
               {
                   if(slowo[j].znak() != ' ')
                   {
                       System.out.print(slowo[j].znak() );
                   }
               }
               //System.out.println( " " + poz + " " + i);
           }
              
             

          
   }
  
  
  
  
  
   static class litera
   {
       int value = 0;
       int max = 4;
       char[] znaki = {' ','a','b','c'};
      
       boolean next(int prev)
       {
           value++;
           if(value == prev)
           {
               value++;
           }
           if(value == max)
           {
               value = 0;
               return true;
           }
           return false;
       }
      
       boolean next()
       {
           value++;
           if(value == max)
           {
               value = 0;
               return true;
           }
           return false;
       }
      
       char znak()
       {
           return znaki[value];
       }
   }
  
}