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
#include <stdio.h>

unsigned long pow2(unsigned long exp)
{
    unsigned long result = 1;
    unsigned long base = 2;

    while (exp)
    {
        if (exp & 1) {
            result *= base;
        }
        exp >>= 1;
        base *= base;
    }

    return result;
}

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

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

unsigned long right_child(unsigned long nr, unsigned long level)
{
        return nr + pow2(level);
}

int main()
{
        unsigned long n, k, npow, nwords, nr, rchild, level;
        char last_letter;

        scanf("%lu %lu\n", &n, &k);

        if (n <= 62) {
                npow = pow2(n);
                nwords = 3*npow-3;

                if (nwords < k) {
                       printf("NIE\n");
                       return 0;
                }

                if (k <= npow-1) {
                        last_letter = 'a';
                } else {
                        if (k <= 2*npow-2) {
                                last_letter = 'b';
                                k -= npow - 1;
                        } else {
                                last_letter = 'c';
                                k -= 2*npow - 2;
                        }
                }
        } else {
                last_letter = 'a';
        }

        printf("%c", last_letter);
        nr = 1;
        level = n-1;

        while (nr != k) {
                if (level > 62) {
                        nr++;
                        last_letter = left_letter(last_letter);
                } else {
                        rchild = right_child(nr, level);
                        if (k < rchild) {
                                nr++;
                                last_letter = left_letter(last_letter);
                        } else {
                                nr = rchild;
                                last_letter = right_letter(last_letter);
                        }
                }
                level--;
                printf("%c", last_letter);
        }
        printf("\n");

        return 0;
}