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#include <bits/stdc++.h>

using namespace std;

int foo(string s) {
    int o = 0;
    for (int i = 0; i < s.length(); o += s[i] - '0', i++);
    return o;
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    
    int n;
    cin >> n;
    string str;
    cin >> str;
    
    int cnt = 0;
    for (auto& c : str) {
        if (cnt == 2*n) {
            break;
        }
        if (c == '1') {
            c = '0';
            cnt++;
        }
    }
    
    if (cnt != 2*n) {
        cout << "NIE\n";
        return 0;
    }
    
    int ones = foo(str);
    vector<int> bits(n);
    
    for (int b = 0; ; b++) {
        if (b == bits.size()) {
            b = 0;
        }
        
        if (ones) {
            bits[b] <<= 1;
            bits[b]++;
            ones--;
        } else {
            break;
        }
    }
    
    for (auto b : bits) {
        if (b > 26 || b == 0) {
            cout << "NIE\n";
            return 0;
        }
    }
    
    for (auto b : bits) {
        cout << (char)(96 + b);
    }
    cout << '\n';

    return 0;
}