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import java.util.Scanner;

public class slo {
    private int signs;
    private int wordNum;

    private void read() {
        Scanner scanner = new Scanner(System.in);
        this.signs = scanner.nextInt();
        this.wordNum = scanner.nextInt();
    }

    private String calculate() {
        int num = wordNum - 1;

        if (inside(num, signs)) {
            return findString('a', num, signs);
        }
        int treeSize = treeSize(signs);

        if (inside(num - treeSize, signs)) {
            return findString('b', num - treeSize, signs);
        } else if (inside(num - 2 * treeSize, signs)) {
            return findString('c', num - 2 * treeSize, signs);
        }
        return "NIE";
    }

    private String findString(char rootChar, int num, int height) {
        String result = String.valueOf(rootChar);

        while (num > 0) {
            num -= 1;
            height -= 1;
            if (inside(num, height)) {
                rootChar = smallerChar(rootChar);
            } else {
                rootChar = biggerChar(rootChar);
                num -= treeSize(height);
            }
            result += rootChar;
        }
        return result;
    }

    private char smallerChar(char c) {
        if (c == 'a') {
            return 'b';
        }
        return 'a';
    }

    private char biggerChar(char c) {
        if (c == 'c') {
            return 'b';
        }
        return 'c';
    }

    private boolean inside(int nodeNr, int treeHeight) {
        int size = 0;
        for (int i = 0; i < treeHeight; i++) {
            size = size * 2 + 1;
            if (size > nodeNr) {
                return true;
            }
        }
        return false;
    }

    private int treeSize(int height) {
        if (height == 1) {
            return 1;
        }
        return 2 * treeSize(height - 1) + 1;
    }

    public static void main(String args[]) {
        slo slo = new slo();
        slo.read();
        System.out.println(slo.calculate());
    }
}