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#include <bits/stdc++.h>
using namespace std;
using LL = long long;
#define e1 first
#define e2 second
#define pb push_back
#define OUT(x) {cout << x << "\n"; exit(0); }
#define TCOUT(x) {cout << x << "\n"; return; }
#define FOR(i, l, r) for(int i = (l); i <= (r); ++i)
#define rep(i, l, r) for(int i = (l); i < (r); ++i)
#define boost {ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0); }
#define sz(x) int(x.size())
#define trav(a, x) for(auto& a : x)
#define all(x) begin(x), end(x)
typedef long long ll;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;
typedef vector<int> vi;
typedef vector<ll> vll;
/*#include <atcoder/modint>
using namespace atcoder;
using mint = modint998244353;
vector <mint> fac, inv;
mint binom(int n, int k) {
	if (n < k || n < 0) return 0;
	return fac[n] * inv[k] * inv[n-k];
}

void prep(int N) {
	fac.resize(N+1, 1); inv.resize(N+1, 1);
	for (int i=1; i<=N; ++i) fac[i] = fac[i-1] * i;
	inv[N] = fac[N].inv();
	for (int i=N-1; i>0; --i) inv[i] = inv[i+1] * (i + 1);
}*/

mt19937_64 rng(time(0));
int random(int l, int r) {
	return uniform_int_distribution<int>(l, r)(rng);
}
#ifdef DEBUG
template<class T> int size(T &&x) {
	return int(x.size());
}
template<class A, class B> ostream& operator<<(ostream &out, const pair<A, B> &p) {
	return out << '(' << p.first << ", " << p.second << ')';
}
template<class T> auto operator<<(ostream &out, T &&x) -> decltype(x.begin(), out) {
	out << '{';
	for(auto it = x.begin(); it != x.end(); ++it)
		out << *it << (it == prev(x.end()) ? "" : ", ");
	return out << '}';
}
void dump() {}
template<class T, class... Args> void dump(T &&x, Args... args) {
	cerr << x << ";  ";
	dump(args...);
}
#endif
#ifdef DEBUG
  struct Nl{~Nl(){cerr << '\n';}};
# define debug(x...) cerr << (strcmp(#x, "") ? #x ":  " : ""), dump(x), Nl(), cerr << ""
#else
# define debug(...) 0 && cerr
#endif
const int maxn = 1000100;

//Did you REAALLY consider sample tests?
void solve() {
	int n;
	cin >> n;
	string s; cin >> s;
	int zer = 0, jed = 0;
	vector <int> znaki(15, 0);
	
	rep(i, 0, 8*n) {
		if (s[i] == '0') ++zer;
		else ++jed;
	}

	int pocz = 'a', kon = 'z';
	FOR(i, pocz, kon) znaki[__builtin_popcount(i)] = i;
	
	int front = 0; while (znaki[front] == 0) ++front;
	int back = 14; while (znaki[back] == 0) --back;
	
	auto ok = [&](int nn, int jedynek) -> bool {
		return front * nn <= jedynek && jedynek <= back * nn;
	};
	
	if (!(ok(n, jed))) TCOUT("NIE");
	string wyn = "";
	int remains = n;
	FOR(step, 1, n) {
		bool flag = false;
		FOR(zabiore, front, back) {
			if (!flag && ok(remains - 1, jed - zabiore)) {
				flag = 1;
				remains--;
				jed -= zabiore;
				wyn += (char)(znaki[zabiore]);
			}
		}
		assert(flag);
	}
	
	assert(sz(wyn) == n);
	cout << wyn << "\n";
	
}

int main() {
	boost;
	int tests;
	//cin >> tests;
	tests = 1;
	FOR(test, 1, tests) {
		solve();
	}
}