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#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <ctime>

#include <vector>
#include <string>
#include <map>
#include <set>
#include <queue>
#include <algorithm>

using namespace std;

#define REP(i, n) for (int i=0, ___=(n); i<___; ++i)
#define FOR(i, a, b) for (int i=(a), ___=(b); i<=___; ++i)
#define FORD(i, a, b) for (int i=(a), ___=(b); i>=___; --i)

typedef pair<int, int> PII;
typedef vector<int> VI;
typedef vector<VI> VVI;

#define mp make_pair
#define ST first
#define ND second

int read() { int n; scanf("%d", &n); return n; }
long long readl() { long long n; scanf("%lld", &n); return n; }

long long cnt(long long n) {
	if (n > 61) n = 61;
	return (3LL << n) - 3;
}

long long cnt2(long long n) {
	if (n > 61) n = 61;
	return (1LL << n) - 1;
}

void foo(long long n, long long k, char c) {
	while (k > 1) {
		--k;
		long long all = cnt2(n);
		if (k <= all) {
			char cc = c == 'a' ? 'b' : 'a';
			printf("%c", cc);
			c = cc;
		} else {
			char cc = c == 'c' ? 'b' : 'c';
			printf("%c", cc);
			c = cc;
			k -= all;
		}
		--n;
	}
	printf("\n");
}

void foo(long long n, long long k)
{
	if (k <= n) {
		while (k >= 2) { printf("ab"); k -= 2; }
		if (k > 0) printf("a");
		printf("\n");
		return;
	}
	long long all = cnt(n);
	if (k > all) {
		printf("NIE\n");
		return;
	}
	all /= 3;
	if (k <= all) {
		printf("a");
		foo(n-1, k, 'a');
		return;
	}
	if (k <= all*2) {
		printf("b");
		foo(n-1, k - all, 'b');
		return;
	}
	printf("c");
	foo(n-1, k - all - all, 'c');
}

void brut(long long n, long long k) {
	vector<string> v;
	v.push_back("");
	v.push_back("a");
	v.push_back("b");
	v.push_back("c");
	for (int i=2; i<=n; ++i) {
		int n = v.size();
		for (int j=0; j<n; ++j) if (v[j].size() == i-1) {
			string s = v[j];
			FOR(c, 'a', 'c') {
				if (s[i-2] == c) continue;
				string ss(s);
				ss.push_back(c);
				v.push_back(ss);
			}
		}
	}
	sort(v.begin(), v.end());
	if (k >= v.size()) printf("NIE\n");
	else printf("%s\n", v[k].c_str());
}

int main()
{
	long long n = readl();
	long long k = readl();
	foo(n, k);
	return 0;
}