#include <bits/stdc++.h>
#define boost ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define debug(x) cerr << #x << " " << x << endl
#define int long long
#define st first
#define nd second

using namespace std;

const int N(1e6 + 13);
const int MAX(LLONG_MAX);

int n, count_bits, hilfe;
bool flag;
string s;

int32_t main() {
  boost;
  cin >> n;
  cin >> s;
  for (int i = 0; i < s.size(); i++) {
    count_bits += s[i] - '0';
  }

  if (count_bits < n * 3 || count_bits > n * 6) {
    cout << "NIE";
  } else {
    if (count_bits % 3 == 1) {
      cout << "x";
      count_bits -= 4;
      n--;
    } else if (count_bits % 3 == 2) {
      cout << "y";
      count_bits -=5;
      n--;
    }

    hilfe = count_bits / 3;
    while (hilfe > n) {
      cout << "w";
      hilfe -= 2;
      n--;
    }

    for (int i = 1; i <= n; i++) {
      cout << "a";
    }

  }
  cout << endl;

}