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#include <bits/stdc++.h>

using namespace std;

#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define reunique(v) v.resize(std::unique(v.begin(), v.end()) - v.begin())
#define sz(v) ((int)(v).size())

#define vec1d(x) vector<x>
#define vec2d(x) vector<vec1d(x)>
#define vec3d(x) vector<vec2d(x)>
#define vec4d(x) vector<vec3d(x)>

#define ivec1d(x, n, v) vec1d(x)(n, v)
#define ivec2d(x, n, m, v) vec2d(x)(n, ivec1d(x, m, v))
#define ivec3d(x, n, m, k, v) vec3d(x)(n, ivec2d(x, m, k, v))
#define ivec4d(x, n, m, k, l, v) vec4d(x)(n, ivec3d(x, m, k, l, v))

#ifdef LOCAL
#include "pretty_print.h"
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]: ", debug_out(__VA_ARGS__)
#else
#define dbg(...) 42
#endif

#define nl "\n"

typedef long double ld;
typedef long long ll;
typedef unsigned long long ull;

template <typename T> T sqr(T x) { return x * x; }
template <typename T> T abs(T x) { return x < 0? -x : x; }
template <typename T> T gcd(T a, T b) { return b? gcd(b, a % b) : a; }
template <typename T> bool chmin(T &x, const T& y) { if (x > y) { x = y; return true; } return false; }
template <typename T> bool chmax(T &x, const T& y) { if (x < y) { x = y; return true; } return false; }

auto random_address = [] { char *p = new char; delete p; return (uint64_t) p; };
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count() * (random_address() | 1));
mt19937_64 rngll(chrono::steady_clock::now().time_since_epoch().count() * (random_address() | 1));


int main(int /* argc */, const char** /* argv */)
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
#ifdef LOCAL
    assert(freopen("i.txt", "r", stdin));
    assert(freopen("o.txt", "w", stdout));
#endif

    int n;
    string s;
    while (cin >> n >> s) {
        int k = 0;
        for (int i = 0; i < sz(s); ++i) {
            k += s[i] == '1';
        }
        map<int, char> m;
        for (char c = 'a'; c <= 'z'; ++c) {
            int t = 0;
            for (int i = 0; i < 8; ++i) {
                t += (c >> i) & 1;
            }
            if (!m.count(t)) {
                m[t] = c;
            }
        }

        int low = m.begin()->first;
        int high = m.rbegin()->first;

        if (k < n * low || n * high < k) {
            cout << "NIE" << nl;
        } else {
            for (int i = 0; i < n; ++i) {
                int z = n - i - 1;
                for (auto& it : m) {
                    int x = it.first;
                    if (z * low <= k - x && k - x <= z * high) {
                        k -= x;
                        cout << it.second;
                        break;
                    }
                }
            }
            cout << nl;
        }
    }

#ifdef LOCAL
    cerr << "Time execute: " << clock() / (double)CLOCKS_PER_SEC << " sec" << endl;
#endif
    return 0;
}