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#include <cstdio>
#include <cmath>
#include <string>

using namespace std;

#define INF 18446744073709551615

typedef unsigned long long ull;

char sections[] = { 'a', 'b', 'c' };

ull sectionSize(int section, int n, int k) {
	n -= section;
	if (n > 64) return INF;
	return pow(2, n) - 1;
}

int whichSection(int depth, int n, int k, bool *first, char prev = ' ') {
	ull size = sectionSize(depth, n, k);
	if (depth == 0) {
		if (k <= size) { return 0; }
		if (k <= 2 * size) { return 1; }
		if (k <= 3 * size) { return 2; }
		return -1;
	}
	*first = k <= size;
	if (prev == sections[0]) {
		return k <= size ? 1 : 2;
	} else if (prev == sections[1]) {
		return k <= size ? 0 : 2;
	} else {
		return k <= size ? 0 : 1;
	}
}
int isFirstn(int isFirst) { if (isFirst) return 0; else return 1; }

int main() {
	ull n, k;
	scanf("%llu %llu", &n, &k);
	string s = "";
	bool isFirst;
	int section = whichSection(0, n, k, &isFirst);
	if (section < 0) { printf("NIE\n"); return 0; }
	s += sections[section];
	int id = 0;
	k -= section * (sectionSize(id, n, k));k--;
	id++;
	while (k > 0) {
		section = whichSection(id, n, k, &isFirst, sections[section]);
		if (section < 0) { printf("NIE\n"); return 0; }
		s += sections[section];
		k--;
		k -= isFirstn(isFirst) * (sectionSize(id, n, k));
		id++;
	}
	printf("%s\n", s.c_str());
	return 0;
}