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#include <cstdio>
#include <algorithm>

#define DEBUG false

using namespace std;

inline long long pow(int a, int b)
{
  long long c = 1;
  while (b--) { c *= a; }
  return c;
}

void rec(long long current, long long k, int prev_letter)
{
  if (current == 0)
    return;

  int n_letter = (prev_letter + 1) % 3, nn_letter = (prev_letter + 2) % 3;
  if (n_letter > nn_letter) {
    swap(n_letter, nn_letter);
  }

  long long mid = current >> 1;
  if (DEBUG) {
    printf("current %lld (mid: %lld); k: %lld\n", current, mid, k);
    printf("letter: %d; %d\n", n_letter, nn_letter);
  }

  if (k == 1) {
    printf("%c", (char)((int)'a' + n_letter));
    return;
  } else if (k == mid + 1) {
    printf("%c", (char)((int)'a' + nn_letter));
    return;
  }

  if (k <= mid) {
    printf("%c", (char)((int)'a' + n_letter));
    rec(mid-1, k-1, n_letter);
  } else {
    printf("%c", (char)((int)'a' + nn_letter));
    rec(mid-1, k-mid-1, nn_letter);
  }
}

int main()
{
  int n;
  long long k;
  scanf("%d %lld", &n, &k);

  long long all = (pow(2, n) - 1);
  if (3*all < k) {
    printf("NIE\n");
    return 0;
  }

  if (DEBUG) {
    printf("all: %lld\n", all);
  }


  // divide by 3 parts
  if (k == 1) {
    printf("a\n");
    return 0;
  } else if (k == all + 1) {
    printf("b\n");
    return 0;
  } else if (k == 2*all + 1) {
    printf("c\n");
    return 0;
  }

  if (k > 1 && k <= all) {
    printf("a");
    rec(all-1, k-1, 0);
  } else if (k > all+1 && k <= 2*all) {
    printf("b");
    rec(all-1, k-all-1, 1);
  } else if (k > 2*all+1 && k <= 3*all) {
    printf("c");
    rec(all-1, k-2*all-1, 2);
  }

  printf("\n");
  return 0;
}