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#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <deque>

using namespace std;

#define LOG if (false) cerr
#define INTERACTIVE true
typedef long long ll;
typedef unsigned long long ull;

const ull INF = 1000000000000000009ull;
const char digit2letter[] = { 'a', 'b', 'c' };


deque<ull> getDividers(int n, ull k)
{
    deque<ull> dividers;
    
    if (n == 1)
    {
        dividers.push_back(1);
    }
    else
    {    
        ull divider = 3;        
        for (int i = 1; i < n; i++)
        {
            dividers.push_back(divider);
            divider = min(divider * 2 + 1, INF);
        }
    }
    
    reverse(dividers.begin(), dividers.end());
    
    return dividers;
}


inline int getNextDigit(int previousDigit, int shift)
{
    int nextDigit = (previousDigit + shift + 1) % 3;
    
    if (previousDigit == 1)
    {
        nextDigit = 2 - nextDigit;
    }
    
    return nextDigit;
}


string solveWhenExists(deque<ull>& dividers, int n, ull k)
{
    string word;
    int shift, digit, previousDigit;
    ull pos;
    
    pos = k + 1;
    previousDigit = -1;
    
    for (ull divider : dividers)
    {
        pos--;
        shift = pos / divider;
        pos = pos % divider;
        digit = getNextDigit(previousDigit, shift);
        word += digit2letter[digit];
        
        LOG << "pos=" << pos << ", shift=" << shift << ", digit=" << digit << endl;
        
        if (pos == 0)
        {
            break;
        }
        
        previousDigit = digit;
    }
    
    if (pos > 0)
    {
        shift = (pos - 1) % 2;
        digit = getNextDigit(previousDigit, shift);
        word += digit2letter[digit];        
    }
    
    return word;
}


string solve(int n, ull k)
{
    k--;
    string word;
    auto dividers = getDividers(n, k);
    
    if (k / dividers.front() >= 3)
    {
        word = "NIE";
    }
    else
    {
        word = solveWhenExists(dividers, n, k);
    }
    
    return word;
}


void test()
{
    int n = 4;
    ull k;
    
    for (k = 1; k <= 47; k++)
    {
        cout << endl << "n=" << n << ", k=" << k << endl << solve(n, k);
    }
}


void run()
{
    int n;
    ull k;
    
    cin >> n >> k;
    string result = solve(n, k);
    cout << result;
}


int main()
{
    if (INTERACTIVE)
    {
        run();
    }
    else
    {
        test();
    }
    return 0;
}