#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>
#include <functional>
#include <set>
#include <ctime>
#include <random>
#include <chrono>
#include <cassert>
#include <tuple>
#include <utility>
using namespace std;

namespace {
  using Integer = long long; //__int128;
  template<class T, class S> istream& operator >> (istream& is, pair<T,S>& p){return is >> p.first >> p.second;}
  template<class T> istream& operator >> (istream& is, vector<T>& vec){for(T& val: vec) is >> val; return is;}
  template<class T> istream& operator ,  (istream& is, T& val){ return is >> val;}
  template<class T, class S> ostream& operator << (ostream& os, const pair<T,S>& p){return os << p.first << " " << p.second;}
  template<class T> ostream& operator << (ostream& os, const vector<T>& vec){for(size_t i=0; i<vec.size(); i++) os << vec[i] << (i==vec.size()-1?"":" "); return os;}
  template<class T> ostream& operator ,  (ostream& os, const T& val){ return os << " " << val;}

  template<class H> void print(const H& head){ cout << head; }
  template<class H, class ... T> void print(const H& head, const T& ... tail){ cout << head << " "; print(tail...); }
  template<class ... T> void println(const T& ... values){ print(values...); cout << endl; }

  template<class H> void eprint(const H& head){ cerr << head; }
  template<class H, class ... T> void eprint(const H& head, const T& ... tail){ cerr << head << " "; eprint(tail...); }
  template<class ... T> void eprintln(const T& ... values){ eprint(values...); cerr << endl; }

  class range{ Integer start_, end_, step_; public: struct range_iterator{ Integer val, step_; range_iterator(Integer v, Integer step) : val(v), step_(step) {} Integer operator * (){return val;} void operator ++ (){val += step_;} bool operator != (range_iterator& x){return step_ > 0 ? val < x.val : val > x.val;} }; range(Integer len) : start_(0), end_(len), step_(1) {} range(Integer start, Integer end) : start_(start), end_(end), step_(1) {} range(Integer start, Integer end, Integer step) : start_(start), end_(end), step_(step) {} range_iterator begin(){ return range_iterator(start_, step_); } range_iterator   end(){ return range_iterator(  end_, step_); } };

  inline string operator "" _s (const char* str, size_t size){ return move(string(str)); }
  constexpr Integer my_pow(Integer x, Integer k, Integer z=1){return k==0 ? z : k==1 ? z*x : (k&1) ? my_pow(x*x,k>>1,z*x) : my_pow(x*x,k>>1,z);}
  constexpr Integer my_pow_mod(Integer x, Integer k, Integer M, Integer z=1){return k==0 ? z%M : k==1 ? z*x%M : (k&1) ? my_pow_mod(x*x%M,k>>1,M,z*x%M) : my_pow_mod(x*x%M,k>>1,M,z);}
  constexpr unsigned long long operator "" _ten (unsigned long long value){ return my_pow(10,value); }

  inline int k_bit(Integer x, int k){return (x>>k)&1;} //0-indexed

  mt19937 mt(chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count());

  template<class T> string join(const vector<T>& v, const string& sep){ stringstream ss; for(size_t i=0; i<v.size(); i++){ if(i>0) ss << sep; ss << v[i]; } return ss.str(); }

  inline string operator * (string s, int k){ string ret; while(k){ if(k&1) ret += s; s += s; k >>= 1; } return ret; }
}
constexpr long long mod = 9_ten + 7;

class SuffixArray{
 public:
  vector<int> sa;
  vector<int> lcp;
  vector<int> rank;

  SuffixArray(const string& SS)
   : S(SS),
     len(SS.size()),
     sa(SS.size()+1),
     lcp(SS.size()+1),
     rank(SS.size()+1)
  {
    constract_sa();
    constract_lcp();
  }

  void dbg_print(){
    for(int i=0; i<=len; i++){
      cerr << S.substr(sa[i]) << " " << lcp[i] << endl;
    }
  }

 private:
  const string& S;
  int len;

  //Manber & Myers
  //O(len (logN)^2)
  void constract_sa(){
    //first character
    for(int i=0; i<=len; i++){
      sa[i] = i;
      rank[i] = (i<len) ? S[i] : -1;
    }

    vector<int> tmp(len+1);
    for(int k=1; k<=len; k *= 2){
      auto cmp_func = [&](int x, int y) -> bool{
        if(rank[x] != rank[y]) return rank[x] < rank[y];
        int l = (x+k <= len) ? rank[x+k] : -1;
        int r = (y+k <= len) ? rank[y+k] : -1;
        return l < r;
      };
      sort(sa.begin(), sa.end(), cmp_func);
      tmp[sa[0]] = 0;
      for(int i=1; i<=len; i++){
        tmp[sa[i]] = tmp[sa[i-1]] + (cmp_func(sa[i-1],sa[i])==true?1:0);
      }
      for(int i=0; i<=len; i++){
        rank[i] = tmp[i];
      }
    }
  }

  void constract_lcp(){
    for(int i=0; i<=len; i++) rank[sa[i]] = i;
    int h=0;
    lcp[0] = 0;
    for(int i=0; i<len; i++){
      int j=sa[rank[i]-1];
      if(h>0) h--;
      for(; j+h<len && i+h<len; h++){
        if(S[j+h] != S[i+h]) break;
      }
      lcp[rank[i] - 1] = h;
    }
  }
};

template<class T=int>
class SparseTable{
 public:
  SparseTable(int len, T default_value_ = 100000000, function<T(T,T)> eval = default_evaluate)
   : col(len), default_value(default_value_) 
  {
    evaluate = eval;
    row = 1;
    while((1<<row) < col) row += 1;
    row++;
    table = vector<vector<T>>(row, vector<T>(col, default_value));
  }

  SparseTable(vector<T>& vec, T default_value_ = 100000000, function<T(T,T)> eval = default_evaluate)
   : col(vec.size()), default_value(default_value_)
  {
    evaluate = eval;

    row = 1;
    while((1<<row) < col) row += 1;
    row++;
    table = vector<vector<T>>(row, vector<T>(col, default_value));

    set(vec);
  }

  void set(vector<T>& vec){
    assert(col == vec.size());

    values = &vec;
    vector<T>& val = vec;

    iota(table[0].begin(), table[0].end(), 0);
    for(int k=1; k<row; k++){
      for(int i=0; i + (1<<k)-1 < col; i++){
        T left = val[table[k-1][i]];
        T right = val[table[k-1][i+(1<<(k-1))]];
        if(left == evaluate(left,right)){
          table[k][i] = table[k-1][i];
        }else{
          table[k][i] = table[k-1][i+(1<<(k-1))];
        }
      }
    }
  }

  //[l,r)
  T get(int l, int r){
    if(l>=r) return default_value;
    vector<T>& val = *values;

    T ret = default_value;

    int k = 0;
    while((1<<(k+1)) < (r-l)) k++;

    T left = val[ table[k][l] ];
    T right = val[ table[k][r-(1<<k)] ];

    ret = evaluate(left, right);
    return ret;
  }

 private:
  int col;
  int row;
  T default_value;
  vector<T>* values;
  vector<vector<T>> table;

  static T default_evaluate(T a, T b){
    return min(a,b);
  }
  function<T(T,T)> evaluate;
};



int main(){
  int k;
  string s;
  cin >> k,s;

  if(k==0){
    println(s);
    return 0;
  }

  int l = (s.size()+k)/(k+1); //l
  int t = s.size()%(k+1);   //cnt l

  if(t==0){
    vector<string> ss(k+1);
    for(int i=0; i<ss.size(); i++){
      ss[i] = s.substr(i*l, l);
    }
    sort(ss.rbegin(), ss.rend());
    println(*ss.begin());
    return 0;
  }

  SuffixArray sa(s);
  SparseTable<int> st(sa.lcp);
  //sa.dbg_print();

  vector<pair<int,int>> r;
  for(int i : range(sa.rank.size()-l)){
    r.push_back({sa.rank[i], i});
  }
  sort(r.begin(), r.end());

  auto check = [&](int x){
    int u = t;
    int v = k+1-t;
    int i;
    for(i=0; i<s.size();){
      if(u && (sa.rank[i] <= r[x].first || st.get(r[x].first, sa.rank[i]) >= l)){
        i += l;
        u--;
      }else{
        if(v>0){
          v--;
          i+=l-1;
        }else{
          return false;
        }
      }
    }
    assert(i==s.size());
    return true;
  };

  long long lb = -1;
  long long ub = r.size()-1;
  while(ub-lb>1){
    long long mid = (lb+ub)/2;
    bool ok = check(mid);
    (ok? ub : lb) = mid;
  }

  println( s.substr(r[ub].second, l) );

  return 0;
}


Measured memory_bytes: 10360