#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

// need
#include <iostream>
#include <algorithm>
// data structure
#include <bitset>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <complex>
//#include <deque>
#include <valarray>
#include <unordered_map>
#include <unordered_set>
#include <array>
// stream
//#include <istream>
#include <sstream>
//#include <ostream>
#include <fstream>
// etc
#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <chrono>
#include <random>
#include <numeric>

// input
#define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
#define VAR(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__);
template<typename T> void MACRO_VAR_Scan(T& t) { std::cin >> t; }
template<typename First, typename...Rest>void MACRO_VAR_Scan(First& first, Rest& ...rest) { std::cin >> first; MACRO_VAR_Scan(rest...); }
#define VEC_ROW(type, n, ...)std::vector<type> __VA_ARGS__;MACRO_VEC_ROW_Init(n, __VA_ARGS__); for(int w_=0; w_<n; ++w_){MACRO_VEC_ROW_Scan(w_, __VA_ARGS__);}
template<typename T> void MACRO_VEC_ROW_Init(int n, T& t) { t.resize(n); }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Init(int n, First& first, Rest& ...rest) { first.resize(n); MACRO_VEC_ROW_Init(n, rest...); }
template<typename T> void MACRO_VEC_ROW_Scan(int p, T& t) { std::cin >> t[p]; }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Scan(int p, First& first, Rest& ...rest) { std::cin >> first[p]; MACRO_VEC_ROW_Scan(p, rest...); }
#define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
#define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& R:c)for(auto& w:R)std::cin>>w;
// output
#define OUT(dist) std::cout<<(dist);
#define FOUT(n, dist) std::cout<<std::fixed<<std::setprecision(n)<<(dist);
#define SOUT(n, c, dist) std::cout<<std::setw(n)<<std::setfill(c)<<(dist);
#define SP std::cout<<" ";
#define TAB std::cout<<"\t";
#define BR std::cout<<"\n";
#define SPBR(w, n) std::cout<<(w + 1 == n ? '\n' : ' ');
#define ENDL std::cout<<std::endl;
#define FLUSH std::cout<<std::flush;
#define SHOW(dist) {std::cerr << #dist << "\t:" << (dist) << "\n";}
#define SHOWVECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOWVECTOR2(v) {std::cerr << #v << "\t:\n";for(const auto& xxx : v){for(const auto& yyy : xxx){std::cerr << yyy << " ";}std::cerr << "\n";}}
#define SHOWQUEUE(a) {auto tmp(a);std::cerr << #a << "\t:";while(!tmp.empty()){std::cerr << tmp.front() << " ";tmp.pop();}std::cerr << "\n";}
// utility
#define ALL(a) (a).begin(),(a).end()
#define FOR(w, a, n) for(int w=(a);w<(n);++w)
#define RFOR(w, a, n) for(int w=(n)-1;w>=(a);--w)
#define REP(w, n) for(int w=0;w<int(n);++w)
#define RREP(w, n) for(int w=int(n)-1;w>=0;--w)
#define IN(a, x, b) (a<=x && x<b)
template<class T> inline T CHMAX(T & a, const T b) { return a = (a < b) ? b : a; }
template<class T> inline T CHMIN(T& a, const T b) { return a = (a > b) ? b : a; }
#define EXCEPTION(msg) throw std::string("Exception : " msg " [ in ") + __func__ + " : " + std::to_string(__LINE__) + " lines ]"
#define TRY(cond, msg) try {if (cond) EXCEPTION(msg);}catch (std::string s) {std::cerr << s << std::endl;}
//void CHECKTIME(std::function<void()> f) { auto start = std::chrono::system_clock::now(); f(); auto end = std::chrono::system_clock::now(); auto res = std::chrono::duration_cast<std::chrono::nanoseconds>((end - start)).count(); std::cerr << "[Time:" << res << "ns  (" << res / (1.0e9) << "s)]\n"; }
// test
template<class T> using V = std::vector<T>;
template<class T> using VV = V<V<T>>;

template<typename S, typename T>
std::ostream& operator<<(std::ostream& os, std::pair<S, T> p) {
	os << "(" << p.first << ", " << p.second << ")"; return os;
}

#define random_shuffle "USE std::shuffle!";

// type/const
//#define int ll
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using PAIR = std::pair<int, int>;
using PAIRLL = std::pair<ll, ll>;
constexpr int INFINT = (1 << 30) - 1;                    // 1.07x10^ 9
constexpr int INFINT_LIM = (1LL << 31) - 1;              // 2.15x10^ 9
constexpr ll INFLL = 1LL << 60;                          // 1.15x10^18
constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62);  // 9.22x10^18
constexpr double EPS = 1e-10;
constexpr int MOD = 1000000007;
constexpr double PI = 3.141592653589793238462643383279;
template<class T, size_t N> void FILL(T(&a)[N], const T & val) { for (auto& x : a) x = val; }
template<class ARY, size_t N, size_t M, class T> void FILL(ARY(&a)[N][M], const T & val) { for (auto& b : a) FILL(b, val); }
template<class T> void FILL(std::vector<T> & a, const T & val) { for (auto& x : a) x = val; }
template<class ARY, class T> void FILL(std::vector<std::vector<ARY>> & a, const T & val) { for (auto& b : a) FILL(b, val); }
// ------------>8------------------------------------->8------------

struct SuffixArray {
private:
	std::vector<int> tmp;
	int n, k;
public:
	std::string s;
	std::vector<int> rank, sa, lcp;
	SuffixArray() {}
	SuffixArray(const std::string& s) : n(s.size()), k(1), s(s), rank(s.size() + 1), sa(s.size() + 1), tmp(s.size() + 1), lcp(s.size() + 1) {
		construct_sa();
		construct_lcp();
	}

	bool compare_sa(int i, int j) {
		if (rank[i] != rank[j]) return rank[i] < rank[j];
		int ri = i + k <= n ? rank[i + k] : -1;
		int rj = j + k <= n ? rank[j + k] : -1;
		return ri < rj;
	}

	void construct_sa() {
		for (int i = 0; i <= n; ++i) {
			sa[i] = i;
			rank[i] = i < n ? s[i] : -1;
		}

		for (k = 1; k <= n; k *= 2) {
			std::sort(sa.begin(), sa.end(), [&](int i, int j) {return compare_sa(i, j); });
			tmp[sa[0]] = 0;
			for (int i = 1; i <= n; ++i) {
				tmp[sa[i]] = tmp[sa[i - 1]] + compare_sa(sa[i - 1], sa[i]);
			}
			for (int i = 0; i <= n; ++i) {
				rank[i] = tmp[i];
			}
		}
	}

	void construct_lcp() {
		for (int i = 0; i <= n; ++i) rank[sa[i]] = i;

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

	// Is T sub-string of S?  O(|T|log|S|)
	bool contain(const std::string & t) {
		int l = 0, r = s.size();
		while (r - l > 1) {
			int m = (l + r) / 2;
			// instead of [s.substr(sa[m], t.size()) < t]
			if (s.compare(sa[m], t.size(), t) < 0) l = m;
			else r = m;
		}
	}

	void debug_show() {
		std::cerr << "idx  " << " sa  " << "LCP  " << "suffix\n";
		for (int i = 0; i < n + 1; ++i) {
			std::cerr << std::setw(3) << std::setfill(' ') << i << "  ";
			std::cerr << std::setw(3) << std::setfill(' ') << sa[i] << "  ";
			std::cerr << std::setw(3) << std::setfill(' ') << lcp[i] << "  ";
			std::cerr << s.substr(sa[i]) << "\n";
		}
	}
};

signed main() {
	INIT;

	VAR(int, k); ++k;
	VAR(std::string, s);
	int n = s.size();

	if (k == 1) {
		OUT(s)BR;
		return 0;
	}
	if (k == n) {
		char c = '1';
		REP(i, n) CHMAX(c, s[i]);
		OUT(c)BR;
		return 0;
	}

	const int L = (n + k - 1) / k;

	SuffixArray sa(s);

	V<int> inv(n + 1);
	REP(i, n + 1) inv[sa.sa[i]] = i;

	int ok = n, ng = 0;
	while (ok - ng > 1) {
		int i = ok + ng >> 1;
		int p = sa.sa[i];

		int now = 0;
		int cnt = 0;
		while (now < n) {
			++cnt;
			if (n - now < L) break;
			if (inv[now] <= i) {
				now += L;
			}
			else {
				now += L - 1;
			}
		}
		if (cnt <= k) ok = i;
		else ng = i;
	}
	OUT(s.substr(sa.sa[ok], L))BR;

	return 0;
}

Measured memory_bytes: 2512