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

long long n,k;
char startchar = 'a';

long long pow2(int n)
{
	long long x = 1;
	while(n)x*=2,n--;
	return x;
}

int main()
{
	scanf("%lld %lld",&n,&k);
	
	long long p = 1;
	
	for(int i=1;i<=n;i++)
	{
		if(p>k)break;
		p*=2;
	}
	
	
	while(k>=p)
	{
		k-=p-1;
		startchar++;
		if(startchar>='d')break;
	}
	
	if(startchar>='d')
	{
		printf("NIE");
		return 0;
	}
	
	long long w=1;
	
	long long m = n-1;
	long long x = -1;
	
	while(w!=k)
	{
		//cout<<w<<' '<<x<<' ';
		putchar(startchar);
		//cout<<endl;
		char c_l,c_r;
		if(startchar == 'a')
			c_l = 'b', c_r = 'c';
		else
		if(startchar == 'b')
			c_l = 'a', c_r = 'c';
		else
		if(startchar == 'c')
			c_l = 'a', c_r = 'b';
		
		
		if(m>60)
		{
			w++;
			startchar = c_l;
			m--;
		}
		else
		{
			if(x == -1)x = pow2(m);
			if(k >= w + x)w += x, startchar = c_r;
			else
			w++, startchar = c_l;
			x/=2;
		}
		
	}
	
	putchar(startchar);
	
	return 0;
}