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#include <iostream>
#include <cmath>

using namespace std;

char jednoZTrzech(unsigned long long n, unsigned long long& k)
{
  if (n > 63)
    {
      return 'a';
    }

  for (char c = 'a'; c < 'd'; ++c)
    {
      if (k <= (1 << n) - 1)
        {
          return c;
        }
      k -= (1 << n) - 1;
    }
  // d jak DUPA
  return 'd';
}

int main()
{
  ios_base::sync_with_stdio(false);

  unsigned long long n, k;

  cin >> n >> k;
  char last = jednoZTrzech(n, k);
  if (last == 'd')
    {
      cout << "NIE" << endl;
      return 0;
    }
  if (k > 0)
    {
      --n;
      while (true)
        {
#ifdef DEBUG
          cerr << "last " << last << " n " << n << " k " << k << endl;
#endif
          cout << last;
          if (k == 1)
            {
              break;
            }
          --k;
          if ((n > 63ull) || ((1ull << n) - 1ull >= k))
            {
              if (last == 'a')
                {
                  last = 'b';
                }
              else
                {
                  last = 'a';
                }
              --n;
              continue;
            }
          else
            {
              if (last == 'c')
                {
                  last = 'b';
                }
              else
                {
                  last = 'c';
                }
              k -= ((1ull << n) - 1ull);
              --n;
              continue;
            }
        }
    }
  cout << endl;

  return 0;
}