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
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

public class slo {
    public static final String NIE = "NIE";
    BufferedReader rd;
    long[] p = new long[1234];
    int ix;

    slo() throws IOException {
        start();
        rd = new BufferedReader(new InputStreamReader(System.in));
        compute();
    }

    private void start() {
        p[1] = 2;
        ix = 1;
        long last = 1L<<61;
        while(p[ix] < last) {
            ix++;
            p[ix] = (p[ix-1] + 1) << 1;
        }
    }

    private void compute() throws IOException {
        long[] a = longarr();
        int n = (int)a[0];
        long k = a[1];
        out(solve(n,k,""));
    }

    private String solve(int n, long k, String s) {
        if(k == 0) {
            return s;
        }
        if(n >= ix) {
            return solve(n-1, k-1, s + next(s, false));
        }
        if(s.isEmpty()) {
            long step = p[n-1]+1;
            char c = 'a';
            while(k > step && c < 'c') {
                k -= step;
                c++;
            }
            if(k > step) {
                return NIE;
            }
            return solve(n-1,k-1,""+c);
        } else {
            long d = p[n] / 2;
            if(k > d) {
                return solve(n - 1, k - d - 1, s + next(s, true));
            } else {
                return solve(n - 1, k - 1, s + next(s, false));
            }
        }
    }

    private char next(String s, boolean up) {
        char c;
        if(s.isEmpty()) {
            c = 'a';
        } else {
            char last = s.charAt(s.length()-1);
            c = last == 'a'?'b':'a';
            if(up) {
                c++;
                if(c == last) {
                    c++;
                }
            }
        }
        return c;
    }

    private long[] longarr() throws IOException {
        return longarr(rd.readLine());
    }

    private long[] longarr(String s) {
        String[] q = split(s);
        int n = q.length;
        long[] a = new long[n];
        for(int i=0;i<n;i++) {
            a[i] = Long.parseLong(q[i]);
        }
        return a;
    }

    public String[] split(String s) {
        if(s == null) {
            return new String[0];
        }
        int n = s.length();
        int start = -1;
        int end = 0;
        int sp = 0;
        boolean lastWhitespace = true;
        for(int i=0;i<n;i++) {
            char c = s.charAt(i);
            if(isWhitespace(c)) {
                lastWhitespace = true;
            } else {
                if(lastWhitespace) {
                    sp++;
                }
                if(start == -1) {
                    start = i;
                }
                end = i;
                lastWhitespace = false;
            }
        }
        if(start == -1) {
            return new String[0];
        }
        String[] res = new String[sp];
        int last = start;
        int x = 0;
        lastWhitespace = true;
        for(int i=start;i<=end;i++) {
            char c = s.charAt(i);
            boolean w = isWhitespace(c);
            if(w && !lastWhitespace) {
                res[x++] = s.substring(last,i);
            } else if(!w && lastWhitespace) {
                last = i;
            }
            lastWhitespace = w;
        }
        res[x] = s.substring(last,end+1);
        return res;
    }

    private boolean isWhitespace(char c) {
        return c==' ' || c=='\t';
    }

    private static void out(Object x) {
        System.out.println(x);
    }

    public static void main(String[] args) throws IOException {
        new slo();
    }
}