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#include<bits/stdc++.h>
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("trapv")

#define st first
#define nd second
#define pb(x) push_back(x)
#define pp(x) pop_back(x)
#define mp(a, b) make_pair(a, b)
#define all(x) (x).begin(), (x).end()
#define rev(x) reverse(all(x))
#define sor(x) sort(all(x))
#define sz(x) (int)(x).size()
#define rsz(x) resize(x)

using namespace std;

///~~~~~~~~~~~~~~~~~~~~~~~~~~

void debug(){cerr<<"\n";}
template <typename H, typename... T>
void debug(H h, T... t) {cerr<<h; if (sizeof...(t)) cerr << ", "; debug(t...);}
#define deb(x...) cerr<<#x<<" = ";debug(x);

///~~~~~~~~~~~~~~~~~~~~~~~~~

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<pii > vii;
typedef vector<ll> vl;
typedef vector<pll> vll;
typedef string str;

#define BOOST ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);

mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());

const int N=2e5+5, INF=1e9+5, mod=1e9+7;

int main(){
	//BOOST;
	int n;
	cin>>n;
	string s;
	cin>>s;
	int a=0, b=0;
	for(char c:s){
		if(c=='0')a++;else b++;}
	a-=2*n;
	b-=3*n;
	if(a<0 || b<0 || b>4*n)cout<<"NIE\n";
	else{
		for(int i=0; i<n; i++){
			if(b>=3){
				cout<<char(96+15);
				b-=3;
			}
			else if(!b)cout<<"a";
			else{
				cout<<char(95+(1<<(b+1)));
				b=0;
			}
		}
	}
}