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#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll Ile[1100000];
const ll MAXLL = 1ll << 60;
ll ileciagow(int len)
{
	return Ile[len];
}
ll ilepusty(int len)
{
	return 1;
}
ll n, k;
char md[] = "baa";
char ma[] = "ccb";
char min_d(char last)
{
	return md[last - 'a'];
}
char max_d(char last)
{
	return ma[last - 'a'];
}
int main()
{
	scanf("%lld%lld", &n, &k);
	
	
	Ile[1] = 1; // ile ciągów z ustalonym pierwszym wyrazem
	for(int i = 2; i <= n; ++i)
	{
		Ile[i] = min(MAXLL, 2 * ileciagow(i-1) + 1);
	}
	
	char l = 'a';
	//pierwsze
	if(Ile[n] + 1 <= k)
	{
		k -= Ile[n] + 1;
		if(Ile[n] <= k)
		{
			k -= Ile[n];
			if(Ile[n] <= k)
			{
				puts("NIE");
				return 0;
			}
			l = 'c';
		}
		else
		{
			l = 'b';
		}
	}
	else
		--k;
	printf("%c", l);
	for(int i = 2; i <= n; ++i)
	{
		if(Ile[n - i + 1] + 1 <= k)
		{
			k -= Ile[n-i+1] + 1;
			l = max_d(l);
		}
		else
		{
			if(k == 0) l = 0;
			else
			{
				l = min_d(l);
				--k;
			}
		}
		if(l != 0)
			printf("%c", l);
	}
	puts("");
}