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#include <iostream>
#include <climits>
using namespace std;

unsigned long long pow(unsigned long long p, unsigned long long w)
{
	unsigned long long r = 1;
	while (w--)
	{
		if (ULLONG_MAX/p<=r)
			return ULLONG_MAX;
		r*=p;
	}
	return r;
}

int main() {
	// your code goes here
	unsigned long long n,k;
	char pop;
	scanf("%llu%llu",&n,&k);
	if(n<=62)
	{
		if(k>3ULL*(pow(2ULL,n)-1ULL)) {printf("NIE\n");return 0;}
		
	}
	if (k<=pow(2ULL,n)-1) pop='a';
	else if (k>2*pow(2ULL,n)-1) pop='c';
	else pop='b';
	printf("%c",pop);
	
	while(k!=1ULL)
	{
		if(k<=pow(2ULL,n-1ULL)-1)
		{
			if(pop=='a') pop = 'b';
			else pop = 'a';
		}
		else
		{
			if(pop=='c') pop = 'b';
			else pop = 'c';
			k-=pow(2ULL,n-1ULL);
		}
		printf("%c",pop);
		n--;
	}
	
	printf("\n");
	return 0;
}