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#include<stdio.h>
#include<string.h>
#include<limits>
void printMin(int * last)
{
    for (int i=0;i<3;i++)
    {
	if(!last[i])
	{
	    memset(last,0,3*sizeof(int));
	    last[i]=1;
	    printf("%c",i+'a');
	    return;
	}
    }
}

void printMax(int * last)
{
    for (int i=2;i>=0;i--)
    {
	if(!last[i])
	{
	    memset(last,0,3*sizeof(int));
	    last[i]=1;
	    printf("%c",i+'a');
	    return;
	}
    }
}

int main()
{
    unsigned long long n,k,max=1;
    scanf("%llu%llu",&n,&k);
    for (int i=0;i<n;i++)
    {
	max*=2;
	if(3*(max-1)>k)break;
    }
    max=3*(max-1);
   
    if(k>max) {printf("NIE\n"); return 0;}

    unsigned long long pot = 1,pot2;
    for (int i =0;i<n;i++)
    {
	pot*=2ULL;
	if(pot-1>=k) 
	{
	    break;
	}
    }
    pot2=pot;
    pot--;
    int last[3]={};
    if(k<=pot) {printf("a"); last[0]=1;}
    else
    {
	pot*=2ULL;
	if(k<=pot) {printf("b"); last[1]=1; k-=(pot/2);}
	else
	{   printf("c"); last[2]=1; k-=pot;}
    }
    k--;
    if(k==0) return 0;
    pot=1;
    for (int i =0;i<n;i++)
    {
	pot*=2;
	if(pot>=k)
	{
	    pot=i+1;
	    break;
	}
    }
    unsigned long long  curPot = 0, curVal=0, pietro =n-1;
    const unsigned long long inf = std::numeric_limits<unsigned long long>::max();
    while(curVal !=k)
    {
	unsigned long long  leftVal = curVal+1,rightVal= inf;
	if(pietro<= pot)
	{
	    rightVal = leftVal + (1ULL<<pietro)-1ULL;
	}
	else
	{
	    curVal =  leftVal;
	    printMin(last);
	    pietro--;
	    continue;
	}
	if(k>=rightVal) 
	{
	    printMax(last);
	    curVal = rightVal;
	}
	else
	{
	    printMin(last);
	    curVal = leftVal;
	}
	pietro--;
    }

//    printf("\n");




    
}