//#define NDEBUG
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <vector>

namespace n91 {

using i8 = std::int_fast8_t;
using i32 = std::int_fast32_t;
using i64 = std::int_fast64_t;
using u8 = std::uint_fast8_t;
using u32 = std::uint_fast32_t;
using u64 = std::uint_fast64_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;

constexpr usize operator"" _z(unsigned long long x) noexcept {
  return static_cast<usize>(x);
}

class rep {
  const usize f, l;

public:
  class itr {
    friend rep;
    usize i;
    constexpr itr(const usize x) noexcept : i(x) {}

  public:
    void operator++() noexcept { ++i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  constexpr rep(const usize first, const usize last) noexcept
      : f(first), l(last) {}
  constexpr itr begin() const noexcept { return itr(f); }
  constexpr itr end() const noexcept { return itr(l); }
};
class revrep {
  const usize f, l;

public:
  class itr {
    friend revrep;
    usize i;
    constexpr itr(usize x) noexcept : i(x) {}

  public:
    void operator++() noexcept { --i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  constexpr revrep(usize first, usize last) noexcept : f(--first), l(--last) {}
  constexpr itr begin() const noexcept { return itr(l); }
  constexpr itr end() const noexcept { return itr(f); }
};
template <class T> using vec_alias = std::vector<T>;
template <class T> auto md_vec(const usize n, const T &value) {
  return std::vector<T>(n, value);
}
template <class... Args> auto md_vec(const usize n, Args... args) {
  return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
}
template <class T> constexpr T difference(const T &a, const T &b) {
  return a < b ? b - a : a - b;
}
template <class T> T scan() {
  T ret;
  std::cin >> ret;
  return ret;
}

} // namespace n91

#include <algorithm>
#include <iostream>
#include <string>
#include <utility>

namespace n91 {

void main_() {
  const usize n = scan<usize>();
  const usize k = scan<usize>();
  const std::string s = scan<std::string>();

  std::string t = s;
  std::reverse(t.begin(), t.end());
  t = s + t;
  std::vector<std::pair<char, usize>> run;
  {
    char prev = '0';
    for (const auto e : t) {
      if (e != prev) {
        prev = e;
        run.emplace_back(e, 0_z);
      }
      ++run.back().second;
    }
  }

  char minc = 'z';
  for (const auto e : t) {
    minc = std::min(minc, e);
  }
  usize maxl = 0_z;
  for (const auto &e : run) {
    if (e.first == minc) {
      maxl = std::max(maxl, e.second);
    }
  }

  usize len = maxl;
  if (len >= n) {
    std::cout << std::string(n, minc) << std::endl;
    return;
  }
  for (const auto i : rep(0_z, k - 1_z)) {
    len *= 2_z;
    if (len >= n) {
      std::cout << std::string(n, minc) << std::endl;
      return;
    }
  }

  const std::string tcomp(maxl, minc);
  std::string minlast(n, 'z');
  for (const auto i : rep(0_z, n + 1_z)) {
    if (t.substr(i, maxl) != tcomp) {
      continue;
    }
    minlast = std::min(minlast, t.substr(i + maxl, n - len));
  }

  std::cout << std::string(len, minc) + minlast << std::endl;
}

} // namespace n91

int main() {
  n91::main_();
  return 0;
}


Measured memory_bytes: 640