#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> l_l;
typedef pair<int, int> i_i;
template<class T>
inline bool chmax(T &a, T b) {
    if(a < b) {
        a = b;
        return true;
    }
    return false;
}

template<class T>
inline bool chmin(T &a, T b) {
    if(a > b) {
        a = b;
        return true;
    }
    return false;
}

#define EPS (1e-7)
#define INF (1e9)
#define PI (acos(-1))
//const ll mod = 1000000007;
ll K;
string S;
struct SuffixArray {
  vector< int > SA;
  const string s;

  SuffixArray(const string &str) : s(str) {
    SA.resize(s.size());
    iota(begin(SA), end(SA), 0);
    sort(begin(SA), end(SA), [&](int a, int b) {
      return s[a] == s[b] ? a > b : s[a] < s[b];
    });
    vector< int > classes(s.size()), c(s.begin(), s.end()), cnt(s.size());
    for(int len = 1; len < s.size(); len <<= 1) {
      for(int i = 0; i < s.size(); i++) {
        if(i > 0 && c[SA[i - 1]] == c[SA[i]] && SA[i - 1] + len < s.size() && c[SA[i - 1] + len / 2] == c[SA[i] + len / 2]) {
          classes[SA[i]] = classes[SA[i - 1]];
        } else {
          classes[SA[i]] = i;
        }
      }
      iota(begin(cnt), end(cnt), 0);
      copy(begin(SA), end(SA), begin(c));
      for(int i = 0; i < s.size(); i++) {
        int s1 = c[i] - len;
        if(s1 >= 0) SA[cnt[classes[s1]]++] = s1;
      }
      classes.swap(c);
    }
  }

  int operator[](int k) const {
    return SA[k];
  }

  size_t size() const {
    return s.size();
  }

  bool lt_substr(const string &t, int si = 0, int ti = 0) {
    int sn = (int) s.size(), tn = (int) t.size();
    while(si < sn && ti < tn) {
      if(s[si] < t[ti]) return true;
      if(s[si] > t[ti]) return false;
      ++si, ++ti;
    }
    return si >= sn && ti < tn;
  }

  int lower_bound(const string &t) {
    int low = -1, high = (int) SA.size();
    while(high - low > 1) {
      int mid = (low + high) / 2;
      if(lt_substr(t, SA[mid])) low = mid;
      else high = mid;
    }
    return high;
  }

  pair< int, int > lower_upper_bound(string &t) {
    int idx = lower_bound(t);
    int low = idx - 1, high = (int) SA.size();
    t.back()++;
    while(high - low > 1) {
      int mid = (low + high) / 2;
      if(lt_substr(t, SA[mid])) low = mid;
      else high = mid;
    }
    t.back()--;
    return {idx, high};
  }

  void output() {
    for(int i = 0; i < size(); i++) {
      cout << i << ": " << s.substr(SA[i]) << endl;
    }
  }
};

struct LongestCommonPrefixArray {
  const SuffixArray &SA;
  vector< int > LCP, rank;

  LongestCommonPrefixArray(const SuffixArray &SA) : SA(SA), LCP(SA.size()) {
    rank.resize(SA.size());
    for(int i = 0; i < SA.size(); i++) {
      rank[SA[i]] = i;
    }
    for(int i = 0, h = 0; i < SA.size(); i++) {
      if(rank[i] + 1 < SA.size()) {
        for(int j = SA[rank[i] + 1]; max(i, j) + h < SA.size() && SA.s[i + h] == SA.s[j + h]; ++h);
        LCP[rank[i] + 1] = h;
        if(h > 0) --h;
      }
    }
  }

  int operator[](int k) const {
    return LCP[k];
  }

  size_t size() const {
    return LCP.size();
  }

  void output() {
    for(int i = 0; i < size(); i++) {
      cout << i << ": " << LCP[i] << " " << SA.s.substr(SA[i]) << endl;
    }
  }
};

int dp[200001];

int main() {
    //cout.precision(10);
    cin.tie(0);
    ios::sync_with_stdio(false);
    cin >> K >> S;
    ll SIZE = (S.size() + K) / (K + 1);
    SuffixArray SA(S);
    int ok = S.size();
    int ng = -1;
    vector<int> inv(S.size());
    for(int i = 0; i < S.size(); i++) {
        inv[SA[i]] = i;
        //cerr << SA[i] << " ";
    }
    //cerr << endl;
    cerr << SIZE << endl;
    while(abs(ok - ng > 1)) {
        int mid = (ok + ng) / 2;
        //cerr << S.substr(SA[mid], SIZE) << endl;
        //cerr << "-----" << mid << "-----" << endl;
        int now = 0;
        for(int i = 0; i <= K; i++) {
            int delta = SIZE-1;
            if(inv[now] <= mid) delta++;
            now += delta;
            //cerr << now << " ";
            if(now >= S.size()) break;
        }
        //cerr << endl;
        if(now >= S.size()) ok = mid;
        else ng = mid;
    }
    //cerr << ok << endl;
    cout << S.substr(SA[ok], SIZE) << endl;
    return 0;
}


Measured memory_bytes: 2000