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#include <iostream>
#include <math.h>
using namespace std;
char first(char c)
{
    if (c=='a') return 'b';
    else return 'a';
}
char second(char c)
{
    if (c=='c') return 'b';
    else return 'c';
}

int main()
{

    long long unsigned int k;
    long long unsigned int n;
    scanf("%lld %lld", &n, &k);


    long long int p ;
    char prev = 'z';
    string output;
    for (int i=0;i<n;i++)
    {
        k--;
        if (n-i>63)
        {
            char k = first(prev);
            output.push_back(k);
            prev = k;
            continue;
        }
        p = pow(2, n-i)-1;
        if (k>=3*p)
        {
            cout << "NIE" << endl;
            return 0;
        }

        if (prev=='z')
        {
            output.push_back(char(int('a') + k/p));
            prev = char(int('a') + k/p);
        }
        else
        {
            if (k/p == 0)
            {
                char k = first(prev);
                output.push_back(k);
                prev = k;
            }
            else
            {
                char k = second(prev);
                output.push_back(k);
                prev = k;
            }
        }
        if (k% p == 0)
        {
            cout << output;
            return 0;
        }
        k = k% p;
    }
    cout << output << endl; 
    return 0;
}