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
#include <iostream>
#include <algorithm>
using namespace std;

long long s[1000001];



// how many good continuations words with <= k characters
void count(int n) {
  s[0] = 1;
  s[1] = 3;
  for (int i = 0; i < n; ++i) {
    if (i > 1) {
      s[i] = 2*s[i-1] + 1;
    }
//    cout << i << " -> " << s[i] << endl;
  }
}

char first(char p) {
  if (p != 'a') return 'a';
  else return 'b';
}

char second(char p) {
  if (!p) return 'b';
  else if (p != 'c') return 'c';
  else return 'b';
}

int main() {
  long long n, k;
  cin >> n >> k;
  count(62);

  char prev = 0;
  if (n < 62 && 3*s[n-1] < k) {
    cout << "NIE" << endl;
    return 0;
  }

  ++k;
  while (n > 0) {
    --k;
    if (k == 0)
      break;
    if (n > 60 || s[n-1] >= k) {
      cout << (prev = first(prev));
    } else if (2*s[n-1] >= k) {
      cout << (prev = second(prev));
      k -= s[n-1];
    } else {
      cout << (prev = 'c');
      k -= 2*s[n-1];
    }
    --n;
  }
  cout << endl;

  return 0;
}