#ifdef _WIN32
#  define LL "%I64d"
#else
#  define LL "%Ld"
#endif

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <ctime>
#include <vector>
#include <deque>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <bitset>
#include <string>
#include <algorithm>
#include <complex>
#include <utility>
#include <cassert>
using namespace std;
#define null NULL
#define mp make_pair
#define pb(a) push_back(a)
#define sz(a) ((int)(a).size())
#define all(a) a.begin() , a.end()
#define fi first
#define se second
#define relaxMin(a , b) (a) = min((a),(b))
#define relaxMax(a , b) (a) = max((a),(b))
#define SQR(a) ((a)*(a))
typedef vector<int> vi;
typedef pair<int,int> pii;
typedef long long ll;
int N , K;
string in;
map<char , int> nal;
string out;
char buf[10000];
int main(){
  freopen("letters.in" , "r" , stdin);
  freopen("letters.out" , "w" , stdout);
  scanf("%d%d" , &N , &K);
  scanf("%s" , &buf);
  in = string(buf);
  for(int i=0;i<sz(in);++i)
   ++nal[in[i]];
  for(map<char,int>::iterator it = nal.begin();
      it != nal.end();
      ++it){
   if(K > 0){
    out += it->fi;
    --it->se;
    --K;
            }
           }
  for(map<char,int>::iterator it = nal.begin();
      it != nal.end();
      ++it){
   while(K > 0 && it->se > 0){
    out += it->fi;
    --it->se;
    --K;
                             }
           }
  sort(all(out));
  printf("%s\n" , out.c_str());
  return 0;
}