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#include <bits/stdc++.h>
#define FOR(i, n) for(int i = 0; i < (n); ++i)
#define REP(i, a, b) for(int i = (a); i < (b); ++i)
#define TRAV(i, a) for(auto & i : (a))
#define SZ(x) ((int)(x).size())
#define X first
#define Y second
#define PR std::pair
#define MP std::make_pair
typedef long long ll;
typedef std::pair<int, int> PII;
typedef std::vector<int> VI;

int main() {
	std::ios_base::sync_with_stdio(false);
	std::cin.tie(0);

	int n;
	std::cin >> n;
	std::string s;
	std::cin >> s;
	VI cnt(2);
	TRAV(i, s) cnt[i-'0']++;
	int balance = cnt[1] - cnt[0];

	std::map<int, char> map;
	FOR(i, 26){
		map[2 * __builtin_popcount('a' + i) - 8] = 'a' + i;
	}

	std::string ans;
	FOR(i, n){
		int want = balance;
		if(want < -2) want = -2;
		if(want > 4) want = 4;
		assert(map.count(want));
		ans += map[want];
		balance -= want;
	}

	if(balance == 0) std::cout << ans << "\n";
	else std::cout << "NIE\n";

	return 0;
}