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import java.util.*;

/**
 * Created by tom on 2016-11-15.
 */
public class slo {

  /**
   * Including the empty word "". Assuming first letter is set.
   */
  private static long getNumberOfWords(long maxLength) {

    return (1L << Math.min(maxLength, 60)) - 1;
  }

  private static String getKthWord(char prevLetter, long maxLength, long k) {

    StringBuilder sb = new StringBuilder("");

    while (k > 0) {

      long numberOfWords = getNumberOfWords(maxLength);

      if (k <= numberOfWords) {
        prevLetter = ('a' == prevLetter) ? 'b' : 'a';
      } else if (k <= 2 * numberOfWords) {
        k -= numberOfWords;
        prevLetter = ('a' == prevLetter || 'b' == prevLetter) ? 'c' : 'b';
      } else if (k <= 3 * numberOfWords) {
        k -= 2 * numberOfWords;
        prevLetter = 'c';
      } else {
        return "NIE";
      }

      sb.append(prevLetter);
      maxLength--;
      k--;
    }

    return sb.toString();
  }

  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    long n = in.nextLong();
    long k = in.nextLong();
    System.out.println(slo.getKthWord('x', n, k));
  }
}