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#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <vector>
#include <stack>
#include <queue>
#include <algorithm>
#include <cmath>
#include <list>
#include <map>
#include <set>
using namespace std;

typedef long long int LL;
typedef long double LD;
typedef vector<int> VI;
typedef vector<LL> VLL;
typedef vector<LD> VLD;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef vector<PII> VPII;

const int INF = 1000000001;
const LD EPS = 10e-9;

#define FOR(x, b, e) for(int x = b; x <= (e); ++x)
#define FORD(x, b, e) for(int x = b; x >= (e); --x)
#define REP(x, n) for(int x = 0; x < (n); ++x)
#define VAR(v, n) __typeof(n) v = (n)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(x) ((int)(x).size())
#define FORE(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define MP make_pair
#define PB push_back
#define ST first
#define ND second
#define abs(a) ((a)<0 ? -(a) : (a))
#define max(a, b) ((a) > (b) ? (a) : (b))
#define min(a, b) ((a) < (b) ? (a) : (b))

const int MAX_POW = 60;

bool reduction;
LL n, k, size;
char lastChar;
char chars[] = {'a', 'b', 'c'};
char nextChar[][2] = {{'b', 'c'}, {'a', 'c'}, {'a', 'b'}};

int main()
{
	ios_base::sync_with_stdio(0);
	
	cin >> n >> k;
	
	k--;
	if(n < MAX_POW && k >= 3*((LL(1)<<n) - 1))
	{
		cout << "NIE" << endl;
		return 0;
	}
	
	if(n >= MAX_POW)
	{
		cout << 'a';
		
		bool a = false;
		while(n >= MAX_POW)
		{
			if(a)
			{
				lastChar = 'a';
				
				cout << lastChar;				
			}
			else
			{
				lastChar = 'b';
				
				cout << lastChar;
			}
			
			a = !a;
			n--;
		}	
		
		reduction = true;
	}	
	
	size = (LL(1)<<n) - 1;
	if(!reduction)
	{
		lastChar = chars[k/size];
		
		cout << lastChar;	
		
		k %= size;
		size = (size-1)/2;
	}
	
	while(k && size)
	{
		k--;
		lastChar = nextChar[lastChar-'a'][k/size];
		
		cout << lastChar;
		
		k %= size;
		size = (size-1)/2;
	}
	
	cout << endl;
	
	return 0;
}