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#include <iostream>
#include <string>

using namespace std;

char selectLower(char c)
{
	switch (c)
	{
		case 'a': return 'b';
		case 'b': return 'a';
		case 'c': return 'a';
	}
}

char selectUpper(char c)
{
	switch (c)
	{
		case 'a': return 'c';
		case 'b': return 'c';
		case 'c': return 'b';
	}
}

int main()
{
	iostream::sync_with_stdio(false);
	cin.tie(NULL);

	int64_t n;
	uint64_t k;
	cin >> n >> k;

	string s = "";
	s.reserve(n);

	uint64_t p = 0;

	if (n >= 60)
	{
		s += 'a';
		n--;
	}
	else
	{
		p = (1 << n);
		int i = 0;
		while (k >= p && i < 3)
		{
			i++;
			k -= p - 1;
		}

		if (i == 3)
		{
			cout << "NIE" << endl;
			return 0;
		}

		s += ('a' + i);
		n--;
	}

	while (k > 1)
	{
		if (n >= 60)
		{
			s += selectLower(s[s.length() - 1]);
			n--;
		}
		else
		{
			p = (1 << n);
			if (k > p)
			{
				k -= p - 1;
				s += selectUpper(s[s.length() - 1]);
			}
			else
			{
				s += selectLower(s[s.length() - 1]);
			}
			n--;
		}
		k--;
	}

	cout << s << endl;
	return 0;
}