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//Mateusz Pabian Jagiellonian University
#include <iostream>
#include <string>
#include <queue>
using namespace std;

queue <char> res;

int main()
{
    long long n,k;
    long long d,last;
    bool f=true;    
    ios_base::sync_with_stdio(0);
    cin >>n>>k;
    if(n<60)
    {
        if( ((1<<n)-1)*3 < k ) f=false; 
    }
    if (f)
    {
        if (n>60) n=60;
        //cout<<"x: "<<n<<endl;
        d=((1L<<n)-1L);
        //cout<<"x: "<<d<<endl;
        if(k<=d) { res.push('a'); last=1; }
        else if(k<=d*2) { res.push('b'); last=2; k-=d;}
        else { res.push('c'); last=3; k-=2*d;}
        int o=20;
        while(k)
        {
            //cout<<"K: "<<k<<endl;
            //cout<<"D: "<<d<<endl;
            if(k==1) break;
            d--;
            d/=2;
            k--;
            if(last==1)
            {
                if(k<=d) {res.push('b'); last=2;}
                else {res.push('c'); last=3; k-=d;}
            }   
            else if(last==2)
            {
                if(k<=d) {res.push('a'); last=1;}
                else {res.push('c'); last=3; k-=d;}
            }
            else
            {
                if(k<=d) {res.push('a'); last=1;}
                else {res.push('b'); last=2; k-=d;}
            }
            //cout<<res.front()<<endl;
        }        
        while(res.empty()==false)
        {
            cout<<res.front();
            res.pop();
        }
        cout<<endl;
    }
    else
    {
        cout<<"NIE"<<endl;
    }     
}