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#include <cstdio>

using namespace std;

long long int k, size = 1;
int n, exp;

void pre() {
  while (exp < n && size - 1 < k) {
    size *= 2;
    ++exp;
  }
  size -= 1;
}

void printLetter(int level, long long int t_size, char letter, long long int node) {
  while (node != k) {
    printf("%c", letter);
    if (level > exp) {
      t_size = level - 1 == exp ? size : 0;
      node += 1;
      letter = letter == 'a' ? 'b' : 'a';
    } else {
      if (k <= node + t_size / 2) {
        letter = letter == 'a' ? 'b' : 'a';
        node += 1;
      } else {
        letter = letter == 'c' ? 'b' : 'c';
        node += t_size / 2 + 1;
      }
      t_size /= 2;
    }
    level -= 1;
  }
  printf("%c\n", letter);
}

void solve() {
  if (exp == n && 3 * size < k) {
    printf("NIE\n");
  } else {
    char l = 'a';
    if (exp == n) {
      l = k > 2 * size ? 'c' : k > size ? 'b' : 'a';
      k -= k > 2 * size ? 2 * size : k > size ? size : 0;
    } 

    printLetter(n, exp < n ? 0 : size, l, 1);
  }
}

void readInput() {
  scanf("%d %lld", &n, &k);
}


int main() {
  readInput();
  pre();
  solve();
  return 0;
}