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#include<bits/stdc++.h>
#define ll long long
#define boost ios_base::sync_with_stdio(false);cin.tie(0);cout.precision(20);
#define inf 1000000000
#define INF 1000000000000000000LL
#define mod 1000000007
#define VI vector<int>
#define PII pair<int, int>
#define st first
#define nd second
#define pb push_back
#define mp make_pair
#define endl '\n'
#define REP(x, y) for(int x = 0; x < (y); ++x)
#define FOR(x, y, z) for(int x = y; x <= (z); ++x)
#define FORR(x, y, z) for(int x = y; x >= (z); --x)
using namespace std;

#define int long long

int n,k,pom;
string wyn;

int pot(int podstawa,int doktorej)
{
	int ans=1;

	FOR(i,1,doktorej)
	{
		ans*=podstawa;
	}

	return ans;
}

#undef int
int main()
{
	boost
	cin >> n >> k;

	if (n<60)
	{
		pom=pot(2,n)-1;
		if (3*pom<k)
		{
			cout << "NIE" << endl;
			return 0;
		}
	}
	else
	{
		pom=pot(2,60)-1;
	}

	if (k<=pom)
	{
		wyn+='a';
	}
	else if (k<=2*pom)
	{
		wyn+='b';
		k-=pom;
	}
	else
	{
		wyn+='c';
		k-=2*pom;
	}
	n--;
	k--;

	while(n>60)
	{
		if (wyn[wyn.size()-1]=='a')
			wyn+='b';
		else
			wyn+='a';
		n--;
		k--;
	}

	//cout << wyn  << " " << n << " " << k << endl;

	while(k)
	{
		pom=pot(2,n)-1;
		if (k>pom)
		{
			if (wyn[wyn.size()-1]=='a')
				wyn+='c';
			else if (wyn[wyn.size()-1]=='b')
				wyn+='c';
			else if (wyn[wyn.size()-1]=='c')
				wyn+='b';
			k-=(pom+1);
		}
		else
		{
			if (wyn[wyn.size()-1]=='a')
				wyn+='b';
			else if (wyn[wyn.size()-1]=='b')
				wyn+='a';
			else if (wyn[wyn.size()-1]=='c')
				wyn+='a';

			k--;
		}
		n--;
	}

	cout << wyn << endl;
  
    return 0;
}