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// Krzysztof Małysa
#include <bits/stdc++.h>
using namespace std;

#define FOR(i,a,n) for (int i = (a), i##__ = (n); i <= i##__; ++i)
#define REP(i,n) FOR(i,0,n-1)
#define FORD(i,a,n) for (int i = (a), i##__ = (n); i >= i##__; --i)
#define ALL(x) x.begin(), x.end()
#define EB emplace_back
#define ST first
#define ND second
#define OO(A) template<class... T> ostream& operator<<(ostream& os, const A<T...>& x) { return __o(os, ALL(x)); }
#define SZ(x) ((int)x.size())

typedef long long LL;
typedef pair<int, int> PII;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<PII> VPII;

template<class A, class B> ostream& operator<<(ostream&, const pair<A, B>&);
template<class I> ostream& __o(ostream&, I, I);
template<class T, size_t N> ostream& operator<<(ostream& os, const array<T, N>& x) { return __o(os, ALL(x)); }
OO(vector) OO(deque) OO(set) OO(multiset) OO(map) OO(multimap)
template<class A, class B> ostream& operator<<(ostream& os, const pair<A, B>& p) {
	return os << "(" << p.ST << ", " << p.ND << ")";
}
template<class I> ostream& __o(ostream& os, I a, I b) {
	os << "{";
	for (; a != b;)
		os << *a++, cerr << (a == b ? "" : " ");
	return os << "}";
}
template<class I> ostream& __d(ostream& os, I a, I b) {
	os << "{\n";
	for (I c = a; a != b; ++a)
		os << "  " << distance(c, a) << ": " << *a << endl;
	return os << "}";
}
template<class... T> void __e(T&&... a) {
	int t[] = {(cerr << forward<T>(a), 0)...}; (void)t;
	cerr << endl;
}

template<class A, class B> void mini(A& a, B&& b) { if (b < a) a = b; }
template<class A, class B> void maxi(A& a, B&& b) { if (b > a) a = b; }
int ceil2(int x) { return 1 << (sizeof(x) * 8 - __builtin_clz(x - 1)); }

#ifdef DEBUG
# define D(...) __VA_ARGS__
#else
# define D(...)
#endif

#define LOG(x) D(cerr << #x ": " << x)
#define LOGN(x) D(LOG(x) << endl)
#define DUMP(x) D(cerr << #x ": ", __d(cerr, ALL(x)) << endl)
#define E(...) D(__e(__VA_ARGS__))
#define endl '\n'
constexpr char nl = '\n';
// End of templates

char lower(char last) { return (last == 'a' ? 'b' : 'a'); }
char upper(char last) { return (last == 'c' ? 'b' : 'c'); }

LL pow2[] = {
	1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768,
	65536, 131072, 262144, 524288, 1048576, 2097152, 4194304, 8388608, 16777216,
	33554432, 67108864, 134217728, 268435456, 536870912, 1073741824, 2147483648,
	4294967296, 8589934592, 17179869184, 34359738368, 68719476736, 137438953472,
	274877906944, 549755813888, 1099511627776, 2199023255552, 4398046511104,
	8796093022208, 17592186044416, 35184372088832, 70368744177664,
	140737488355328, 281474976710656, 562949953421312, 1125899906842624,
	2251799813685248, 4503599627370496, 9007199254740992, 18014398509481984,
	36028797018963968, 72057594037927936, 144115188075855872,
	288230376151711744, 576460752303423488, 1152921504606846976
};

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);


	int n;
	LL k;
	cin >> n >> k;
	// w[i] = 2**i
	string res;
	constexpr int MAX_POT2 = 60;
	if (n > MAX_POT2) {
		res = 'a';
		while (--k, --n > MAX_POT2 && k)
			res += lower(res.back());
	}

	if (res.empty()) {
		if (k < pow2[n]) {
			res = 'a';
			--k;
		} else if (k < 2 * pow2[n] - 1) {
			res = 'b';
			k -= pow2[n];
		} else if (k < 3 * pow2[n] - 2) {
			k -= 2 * pow2[n] - 1;
			res = 'c';
		} else
			return puts("NIE"), 0;
		--n;
	}

	LOGN(res);
	LOGN(n);

	while (n && k) {
		if (k < pow2[n]) {
			res += lower(res.back());
			--k;
		} else {
			k -= pow2[n];
			res += upper(res.back());
		}
		--n;
	}

	LOGN(k);
	LOGN(res);
	assert(k == 0);

	cout << res << nl;
	return 0;
}