1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
import java.util.*;


public class slo {
    private final String letters = "abc";
    private final int MAX = 61;

    private boolean ltcmp(long k, long n) {
        if(n >= MAX) return true;
        return k <= (1L<<n) - 1;
    }

    private String calc(long n, long k) {
        if(n <= MAX && k > 3L*((1L<<n) - 1)) 
            return "NIE";

        int len = 0;
        char[] res = new char[(int)n];

        for(int i=0; i < 3; i++) {
            if(ltcmp(k,n)) {
                res[len++] = letters.charAt(i);
                break;
            } else {
                k -= (1L<<n) - 1;
            }
        }

        n--;

        char c = 'x';
        while(k > 1) {
            k -= 1;
            if(ltcmp(k,n)) {
                c = (res[len-1] == 'a') ? 'b' : 'a';
            } else {
                k -= (1L<<n) - 1;
                c = (res[len-1] == 'c') ? 'b' : 'c';
            }

            res[len++] = c;
            n--;
        }

        return String.valueOf(res, 0, len);
    }

    public static void main(String[] args) {
        slo s = new slo();
        Scanner sc = new Scanner(System.in);
        long n = sc.nextLong();
        long k = sc.nextLong();

        System.out.println(s.calc(n,k));
    }
}